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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * kernel/lockdep.c
  *
  * Runtime locking correctness validator
  *
  * Started by Ingo Molnar:
  *
  *  Copyright (C) 2006,2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
  *
  * this code maps all the lock dependencies as they occur in a live kernel
  * and will warn about the following classes of locking bugs:
  *
  * - lock inversion scenarios
  * - circular lock dependencies
  * - hardirq/softirq safe/unsafe locking bugs
  *
  * Bugs are reported even if the current locking scenario does not cause
  * any deadlock at this point.
  *
  * I.e. if anytime in the past two locks were taken in a different order,
  * even if it happened for another task, even if those were different
  * locks (but of the same class as this lock), this code will detect it.
  *
  * Thanks to Arjan van de Ven for coming up with the initial idea of
  * mapping lock dependencies runtime.
  */
 #define DISABLE_BRANCH_PROFILING
 #include <linux/mutex.h>
 #include <linux/sched.h>
 #include <linux/sched/clock.h>
 #include <linux/sched/task.h>
 #include <linux/sched/mm.h>
 #include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/spinlock.h>
 #include <linux/kallsyms.h>
 #include <linux/interrupt.h>
 #include <linux/stacktrace.h>
 #include <linux/debug_locks.h>
 #include <linux/irqflags.h>
 #include <linux/utsname.h>
 #include <linux/hash.h>
 #include <linux/ftrace.h>
 #include <linux/stringify.h>
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
 #include <linux/gfp.h>
 #include <linux/random.h>
 #include <linux/jhash.h>
 #include <linux/nmi.h>
 #include <linux/rcupdate.h>
 #include <linux/kprobes.h>
 #include <linux/lockdep.h>
 
 #include <asm/sections.h>
 
 #include "lockdep_internals.h"
 
 #include <trace/events/lock.h>
 
 #ifdef CONFIG_PROVE_LOCKING
 static int prove_locking = 1;
 module_param(prove_locking, int, 0644);
 #else
 #define prove_locking 0
 #endif
 
 #ifdef CONFIG_LOCK_STAT
 static int lock_stat = 1;
 module_param(lock_stat, int, 0644);
 #else
 #define lock_stat 0
 #endif
 
 #ifdef CONFIG_SYSCTL
 static struct ctl_table kern_lockdep_table[] = {
 #ifdef CONFIG_PROVE_LOCKING
     {
         .procname       = "prove_locking",
         .data           = &prove_locking,
         .maxlen         = sizeof(int),
         .mode           = 0644,
         .proc_handler   = proc_dointvec,
     },
 #endif /* CONFIG_PROVE_LOCKING */
 #ifdef CONFIG_LOCK_STAT
     {
         .procname       = "lock_stat",
         .data           = &lock_stat,
         .maxlen         = sizeof(int),
         .mode           = 0644,
         .proc_handler   = proc_dointvec,
     },
 #endif /* CONFIG_LOCK_STAT */
     { }
 };
 
 static __init int kernel_lockdep_sysctls_init(void)
 {
     register_sysctl_init("kernel", kern_lockdep_table);
     return 0;
 }
 late_initcall(kernel_lockdep_sysctls_init);
 #endif /* CONFIG_SYSCTL */
 
 DEFINE_PER_CPU(unsigned int, lockdep_recursion);
 EXPORT_PER_CPU_SYMBOL_GPL(lockdep_recursion);
 
 static __always_inline bool lockdep_enabled(void)
 {
     if (!debug_locks)
         return false;
 
     if (this_cpu_read(lockdep_recursion))
         return false;
 
     if (current->lockdep_recursion)
         return false;
 
     return true;
 }
 
 /*
  * lockdep_lock: protects the lockdep graph, the hashes and the
  *               class/list/hash allocators.
  *
  * This is one of the rare exceptions where it's justified
  * to use a raw spinlock - we really dont want the spinlock
  * code to recurse back into the lockdep code...
  */
 static arch_spinlock_t __lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
 static struct task_struct *__owner;
 
 static inline void lockdep_lock(void)
 {
     DEBUG_LOCKS_WARN_ON(!irqs_disabled());
 
     __this_cpu_inc(lockdep_recursion);
     arch_spin_lock(&__lock);
     __owner = current;
 }
 
 static inline void lockdep_unlock(void)
 {
     DEBUG_LOCKS_WARN_ON(!irqs_disabled());
 
     if (debug_locks && DEBUG_LOCKS_WARN_ON(__owner != current))
         return;
 
     __owner = NULL;
     arch_spin_unlock(&__lock);
     __this_cpu_dec(lockdep_recursion);
 }
 
 static inline bool lockdep_assert_locked(void)
 {
     return DEBUG_LOCKS_WARN_ON(__owner != current);
 }
 
 static struct task_struct *lockdep_selftest_task_struct;
 
 
 static int graph_lock(void)
 {
     lockdep_lock();
     /*
      * Make sure that if another CPU detected a bug while
      * walking the graph we dont change it (while the other
      * CPU is busy printing out stuff with the graph lock
      * dropped already)
      */
     if (!debug_locks) {
         lockdep_unlock();
         return 0;
     }
     return 1;
 }
 
 static inline void graph_unlock(void)
 {
     lockdep_unlock();
 }
 
 /*
  * Turn lock debugging off and return with 0 if it was off already,
  * and also release the graph lock:
  */
 static inline int debug_locks_off_graph_unlock(void)
 {
     int ret = debug_locks_off();
 
     lockdep_unlock();
 
     return ret;
 }
 
 unsigned long nr_list_entries;
 static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];
 static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES);
 
 /*
  * All data structures here are protected by the global debug_lock.
  *
  * nr_lock_classes is the number of elements of lock_classes[] that is
  * in use.
  */
 #define KEYHASH_BITS        (MAX_LOCKDEP_KEYS_BITS - 1)
 #define KEYHASH_SIZE        (1UL << KEYHASH_BITS)
 static struct hlist_head lock_keys_hash[KEYHASH_SIZE];
 unsigned long nr_lock_classes;
 unsigned long nr_zapped_classes;
 unsigned long max_lock_class_idx;
 struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
 DECLARE_BITMAP(lock_classes_in_use, MAX_LOCKDEP_KEYS);
 
 static inline struct lock_class *hlock_class(struct held_lock *hlock)
 {
     unsigned int class_idx = hlock->class_idx;
 
     /* Don't re-read hlock->class_idx, can't use READ_ONCE() on bitfield */
     barrier();
 
     if (!test_bit(class_idx, lock_classes_in_use)) {
         /*
          * Someone passed in garbage, we give up.
          */
         DEBUG_LOCKS_WARN_ON(1);
         return NULL;
     }
 
     /*
      * At this point, if the passed hlock->class_idx is still garbage,
      * we just have to live with it
      */
     return lock_classes + class_idx;
 }
 
 #ifdef CONFIG_LOCK_STAT
 static DEFINE_PER_CPU(struct lock_class_stats[MAX_LOCKDEP_KEYS], cpu_lock_stats);
 
 static inline u64 lockstat_clock(void)
 {
     return local_clock();
 }
 
 static int lock_point(unsigned long points[], unsigned long ip)
 {
     int i;
 
     for (i = 0; i < LOCKSTAT_POINTS; i++) {
         if (points[i] == 0) {
             points[i] = ip;
             break;
         }
         if (points[i] == ip)
             break;
     }
 
     return i;
 }
 
 static void lock_time_inc(struct lock_time *lt, u64 time)
 {
     if (time > lt->max)
         lt->max = time;
 
     if (time < lt->min || !lt->nr)
         lt->min = time;
 
     lt->total += time;
     lt->nr++;
 }
 
 static inline void lock_time_add(struct lock_time *src, struct lock_time *dst)
 {
     if (!src->nr)
         return;
 
     if (src->max > dst->max)
         dst->max = src->max;
 
     if (src->min < dst->min || !dst->nr)
         dst->min = src->min;
 
     dst->total += src->total;
     dst->nr += src->nr;
 }
 
 struct lock_class_stats lock_stats(struct lock_class *class)
 {
     struct lock_class_stats stats;
     int cpu, i;
 
     memset(&stats, 0, sizeof(struct lock_class_stats));
     for_each_possible_cpu(cpu) {
         struct lock_class_stats *pcs =
             &per_cpu(cpu_lock_stats, cpu)[class - lock_classes];
 
         for (i = 0; i < ARRAY_SIZE(stats.contention_point); i++)
             stats.contention_point[i] += pcs->contention_point[i];
 
         for (i = 0; i < ARRAY_SIZE(stats.contending_point); i++)
             stats.contending_point[i] += pcs->contending_point[i];
 
         lock_time_add(&pcs->read_waittime, &stats.read_waittime);
         lock_time_add(&pcs->write_waittime, &stats.write_waittime);
 
         lock_time_add(&pcs->read_holdtime, &stats.read_holdtime);
         lock_time_add(&pcs->write_holdtime, &stats.write_holdtime);
 
         for (i = 0; i < ARRAY_SIZE(stats.bounces); i++)
             stats.bounces[i] += pcs->bounces[i];
     }
 
     return stats;
 }
 
 void clear_lock_stats(struct lock_class *class)
 {
     int cpu;
 
     for_each_possible_cpu(cpu) {
         struct lock_class_stats *cpu_stats =
             &per_cpu(cpu_lock_stats, cpu)[class - lock_classes];
 
         memset(cpu_stats, 0, sizeof(struct lock_class_stats));
     }
     memset(class->contention_point, 0, sizeof(class->contention_point));
     memset(class->contending_point, 0, sizeof(class->contending_point));
 }
 
 static struct lock_class_stats *get_lock_stats(struct lock_class *class)
 {
     return &this_cpu_ptr(cpu_lock_stats)[class - lock_classes];
 }
 
 static void lock_release_holdtime(struct held_lock *hlock)
 {
     struct lock_class_stats *stats;
     u64 holdtime;
 
     if (!lock_stat)
         return;
 
     holdtime = lockstat_clock() - hlock->holdtime_stamp;
 
     stats = get_lock_stats(hlock_class(hlock));
     if (hlock->read)
         lock_time_inc(&stats->read_holdtime, holdtime);
     else
         lock_time_inc(&stats->write_holdtime, holdtime);
 }
 #else
 static inline void lock_release_holdtime(struct held_lock *hlock)
 {
 }
 #endif
 
 /*
  * We keep a global list of all lock classes. The list is only accessed with
  * the lockdep spinlock lock held. free_lock_classes is a list with free
  * elements. These elements are linked together by the lock_entry member in
  * struct lock_class.
  */
 static LIST_HEAD(all_lock_classes);
 static LIST_HEAD(free_lock_classes);
 
 /**
  * struct pending_free - information about data structures about to be freed
  * @zapped: Head of a list with struct lock_class elements.
  * @lock_chains_being_freed: Bitmap that indicates which lock_chains[] elements
  *  are about to be freed.
  */
 struct pending_free {
     struct list_head zapped;
     DECLARE_BITMAP(lock_chains_being_freed, MAX_LOCKDEP_CHAINS);
 };
 
 /**
  * struct delayed_free - data structures used for delayed freeing
  *
  * A data structure for delayed freeing of data structures that may be
  * accessed by RCU readers at the time these were freed.
  *
  * @rcu_head:  Used to schedule an RCU callback for freeing data structures.
  * @index:     Index of @pf to which freed data structures are added.
  * @scheduled: Whether or not an RCU callback has been scheduled.
  * @pf:        Array with information about data structures about to be freed.
  */
 static struct delayed_free {
     struct rcu_head     rcu_head;
     int         index;
     int         scheduled;
     struct pending_free pf[2];
 } delayed_free;
 
 /*
  * The lockdep classes are in a hash-table as well, for fast lookup:
  */
 #define CLASSHASH_BITS      (MAX_LOCKDEP_KEYS_BITS - 1)
 #define CLASSHASH_SIZE      (1UL << CLASSHASH_BITS)
 #define __classhashfn(key)  hash_long((unsigned long)key, CLASSHASH_BITS)
 #define classhashentry(key) (classhash_table + __classhashfn((key)))
 
 static struct hlist_head classhash_table[CLASSHASH_SIZE];
 
 /*
  * We put the lock dependency chains into a hash-table as well, to cache
  * their existence:
  */
 #define CHAINHASH_BITS      (MAX_LOCKDEP_CHAINS_BITS-1)
 #define CHAINHASH_SIZE      (1UL << CHAINHASH_BITS)
 #define __chainhashfn(chain)    hash_long(chain, CHAINHASH_BITS)
 #define chainhashentry(chain)   (chainhash_table + __chainhashfn((chain)))
 
 static struct hlist_head chainhash_table[CHAINHASH_SIZE];
 
 /*
  * the id of held_lock
  */
 static inline u16 hlock_id(struct held_lock *hlock)
 {
     BUILD_BUG_ON(MAX_LOCKDEP_KEYS_BITS + 2 > 16);
 
     return (hlock->class_idx | (hlock->read << MAX_LOCKDEP_KEYS_BITS));
 }
 
 static inline unsigned int chain_hlock_class_idx(u16 hlock_id)
 {
     return hlock_id & (MAX_LOCKDEP_KEYS - 1);
 }
 
 /*
  * The hash key of the lock dependency chains is a hash itself too:
  * it's a hash of all locks taken up to that lock, including that lock.
  * It's a 64-bit hash, because it's important for the keys to be
  * unique.
  */
 static inline u64 iterate_chain_key(u64 key, u32 idx)
 {
     u32 k0 = key, k1 = key >> 32;
 
     __jhash_mix(idx, k0, k1); /* Macro that modifies arguments! */
 
     return k0 | (u64)k1 << 32;
 }
 
 void lockdep_init_task(struct task_struct *task)
 {
     task->lockdep_depth = 0; /* no locks held yet */
     task->curr_chain_key = INITIAL_CHAIN_KEY;
     task->lockdep_recursion = 0;
 }
 
 static __always_inline void lockdep_recursion_inc(void)
 {
     __this_cpu_inc(lockdep_recursion);
 }
 
 static __always_inline void lockdep_recursion_finish(void)
 {
     if (WARN_ON_ONCE(__this_cpu_dec_return(lockdep_recursion)))
         __this_cpu_write(lockdep_recursion, 0);
 }
 
 void lockdep_set_selftest_task(struct task_struct *task)
 {
     lockdep_selftest_task_struct = task;
 }
 
 /*
  * Debugging switches:
  */
 
 #define VERBOSE         0
 #define VERY_VERBOSE        0
 
 #if VERBOSE
 # define HARDIRQ_VERBOSE    1
 # define SOFTIRQ_VERBOSE    1
 #else
 # define HARDIRQ_VERBOSE    0
 # define SOFTIRQ_VERBOSE    0
 #endif
 
 #if VERBOSE || HARDIRQ_VERBOSE || SOFTIRQ_VERBOSE
 /*
  * Quick filtering for interesting events:
  */
 static int class_filter(struct lock_class *class)
 {
 #if 0
     /* Example */
     if (class->name_version == 1 &&
             !strcmp(class->name, "lockname"))
         return 1;
     if (class->name_version == 1 &&
             !strcmp(class->name, "&struct->lockfield"))
         return 1;
 #endif
     /* Filter everything else. 1 would be to allow everything else */
     return 0;
 }
 #endif
 
 static int verbose(struct lock_class *class)
 {
 #if VERBOSE
     return class_filter(class);
 #endif
     return 0;
 }
 
 static void print_lockdep_off(const char *bug_msg)
 {
     printk(KERN_DEBUG "%s\n", bug_msg);
     printk(KERN_DEBUG "turning off the locking correctness validator.\n");
 #ifdef CONFIG_LOCK_STAT
     printk(KERN_DEBUG "Please attach the output of /proc/lock_stat to the bug report\n");
 #endif
 }
 
 unsigned long nr_stack_trace_entries;
 
 #ifdef CONFIG_PROVE_LOCKING
 /**
  * struct lock_trace - single stack backtrace
  * @hash_entry: Entry in a stack_trace_hash[] list.
  * @hash:   jhash() of @entries.
  * @nr_entries: Number of entries in @entries.
  * @entries:    Actual stack backtrace.
  */
 struct lock_trace {
     struct hlist_node   hash_entry;
     u32         hash;
     u32         nr_entries;
     unsigned long       entries[] __aligned(sizeof(unsigned long));
 };
 #define LOCK_TRACE_SIZE_IN_LONGS                \
     (sizeof(struct lock_trace) / sizeof(unsigned long))
 /*
  * Stack-trace: sequence of lock_trace structures. Protected by the graph_lock.
  */
 static unsigned long stack_trace[MAX_STACK_TRACE_ENTRIES];
 static struct hlist_head stack_trace_hash[STACK_TRACE_HASH_SIZE];
 
 static bool traces_identical(struct lock_trace *t1, struct lock_trace *t2)
 {
     return t1->hash == t2->hash && t1->nr_entries == t2->nr_entries &&
         memcmp(t1->entries, t2->entries,
                t1->nr_entries * sizeof(t1->entries[0])) == 0;
 }
 
 static struct lock_trace *save_trace(void)
 {
     struct lock_trace *trace, *t2;
     struct hlist_head *hash_head;
     u32 hash;
     int max_entries;
 
     BUILD_BUG_ON_NOT_POWER_OF_2(STACK_TRACE_HASH_SIZE);
     BUILD_BUG_ON(LOCK_TRACE_SIZE_IN_LONGS >= MAX_STACK_TRACE_ENTRIES);
 
     trace = (struct lock_trace *)(stack_trace + nr_stack_trace_entries);
     max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries -
         LOCK_TRACE_SIZE_IN_LONGS;
 
     if (max_entries <= 0) {
         if (!debug_locks_off_graph_unlock())
             return NULL;
 
         print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!");
         dump_stack();
 
         return NULL;
     }
     trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3);
 
     hash = jhash(trace->entries, trace->nr_entries *
              sizeof(trace->entries[0]), 0);
     trace->hash = hash;
     hash_head = stack_trace_hash + (hash & (STACK_TRACE_HASH_SIZE - 1));
     hlist_for_each_entry(t2, hash_head, hash_entry) {
         if (traces_identical(trace, t2))
             return t2;
     }
     nr_stack_trace_entries += LOCK_TRACE_SIZE_IN_LONGS + trace->nr_entries;
     hlist_add_head(&trace->hash_entry, hash_head);
 
     return trace;
 }
 
 /* Return the number of stack traces in the stack_trace[] array. */
 u64 lockdep_stack_trace_count(void)
 {
     struct lock_trace *trace;
     u64 c = 0;
     int i;
 
     for (i = 0; i < ARRAY_SIZE(stack_trace_hash); i++) {
         hlist_for_each_entry(trace, &stack_trace_hash[i], hash_entry) {
             c++;
         }
     }
 
     return c;
 }
 
 /* Return the number of stack hash chains that have at least one stack trace. */
 u64 lockdep_stack_hash_count(void)
 {
     u64 c = 0;
     int i;
 
     for (i = 0; i < ARRAY_SIZE(stack_trace_hash); i++)
         if (!hlist_empty(&stack_trace_hash[i]))
             c++;
 
     return c;
 }
 #endif
 
 unsigned int nr_hardirq_chains;
 unsigned int nr_softirq_chains;
 unsigned int nr_process_chains;
 unsigned int max_lockdep_depth;
 
 #ifdef CONFIG_DEBUG_LOCKDEP
 /*
  * Various lockdep statistics:
  */
 DEFINE_PER_CPU(struct lockdep_stats, lockdep_stats);
 #endif
 
 #ifdef CONFIG_PROVE_LOCKING
 /*
  * Locking printouts:
  */
 
 #define __USAGE(__STATE)                        \
     [LOCK_USED_IN_##__STATE] = "IN-"__stringify(__STATE)"-W",   \
     [LOCK_ENABLED_##__STATE] = __stringify(__STATE)"-ON-W",     \
     [LOCK_USED_IN_##__STATE##_READ] = "IN-"__stringify(__STATE)"-R",\
     [LOCK_ENABLED_##__STATE##_READ] = __stringify(__STATE)"-ON-R",
 
 static const char *usage_str[] =
 {
 #define LOCKDEP_STATE(__STATE) __USAGE(__STATE)
 #include "lockdep_states.h"
 #undef LOCKDEP_STATE
     [LOCK_USED] = "INITIAL USE",
     [LOCK_USED_READ] = "INITIAL READ USE",
     /* abused as string storage for verify_lock_unused() */
     [LOCK_USAGE_STATES] = "IN-NMI",
 };
 #endif
 
 const char *__get_key_name(const struct lockdep_subclass_key *key, char *str)
 {
     return kallsyms_lookup((unsigned long)key, NULL, NULL, NULL, str);
 }
 
 static inline unsigned long lock_flag(enum lock_usage_bit bit)
 {
     return 1UL << bit;
 }
 
 static char get_usage_char(struct lock_class *class, enum lock_usage_bit bit)
 {
     /*
      * The usage character defaults to '.' (i.e., irqs disabled and not in
      * irq context), which is the safest usage category.
      */
     char c = '.';
 
     /*
      * The order of the following usage checks matters, which will
      * result in the outcome character as follows:
      *
      * - '+': irq is enabled and not in irq context
      * - '-': in irq context and irq is disabled
      * - '?': in irq context and irq is enabled
      */
     if (class->usage_mask & lock_flag(bit + LOCK_USAGE_DIR_MASK)) {
         c = '+';
         if (class->usage_mask & lock_flag(bit))
             c = '?';
     } else if (class->usage_mask & lock_flag(bit))
         c = '-';
 
     return c;
 }
 
 void get_usage_chars(struct lock_class *class, char usage[LOCK_USAGE_CHARS])
 {
     int i = 0;
 
 #define LOCKDEP_STATE(__STATE)                      \
     usage[i++] = get_usage_char(class, LOCK_USED_IN_##__STATE); \
     usage[i++] = get_usage_char(class, LOCK_USED_IN_##__STATE##_READ);
 #include "lockdep_states.h"
 #undef LOCKDEP_STATE
 
     usage[i] = '\0';
 }
 
 static void __print_lock_name(struct lock_class *class)
 {
     char str[KSYM_NAME_LEN];
     const char *name;
 
     name = class->name;
     if (!name) {
         name = __get_key_name(class->key, str);
         printk(KERN_CONT "%s", name);
     } else {
         printk(KERN_CONT "%s", name);
         if (class->name_version > 1)
             printk(KERN_CONT "#%d", class->name_version);
         if (class->subclass)
             printk(KERN_CONT "/%d", class->subclass);
     }
 }
 
 static void print_lock_name(struct lock_class *class)
 {
     char usage[LOCK_USAGE_CHARS];
 
     get_usage_chars(class, usage);
 
     printk(KERN_CONT " (");
     __print_lock_name(class);
     printk(KERN_CONT "){%s}-{%d:%d}", usage,
             class->wait_type_outer ?: class->wait_type_inner,
             class->wait_type_inner);
 }
 
 static void print_lockdep_cache(struct lockdep_map *lock)
 {
     const char *name;
     char str[KSYM_NAME_LEN];
 
     name = lock->name;
     if (!name)
         name = __get_key_name(lock->key->subkeys, str);
 
     printk(KERN_CONT "%s", name);
 }
 
 static void print_lock(struct held_lock *hlock)
 {
     /*
      * We can be called locklessly through debug_show_all_locks() so be
      * extra careful, the hlock might have been released and cleared.
      *
      * If this indeed happens, lets pretend it does not hurt to continue
      * to print the lock unless the hlock class_idx does not point to a
      * registered class. The rationale here is: since we don't attempt
      * to distinguish whether we are in this situation, if it just
      * happened we can't count on class_idx to tell either.
      */
     struct lock_class *lock = hlock_class(hlock);
 
     if (!lock) {
         printk(KERN_CONT "<RELEASED>\n");
         return;
     }
 
     printk(KERN_CONT "%px", hlock->instance);
     print_lock_name(lock);
     printk(KERN_CONT ", at: %pS\n", (void *)hlock->acquire_ip);
 }
 
 static void lockdep_print_held_locks(struct task_struct *p)
 {
     int i, depth = READ_ONCE(p->lockdep_depth);
 
     if (!depth)
         printk("no locks held by %s/%d.\n", p->comm, task_pid_nr(p));
     else
         printk("%d lock%s held by %s/%d:\n", depth,
                depth > 1 ? "s" : "", p->comm, task_pid_nr(p));
     /*
      * It's not reliable to print a task's held locks if it's not sleeping
      * and it's not the current task.
      */
     if (p != current && task_is_running(p))
         return;
     for (i = 0; i < depth; i++) {
         printk(" #%d: ", i);
         print_lock(p->held_locks + i);
     }
 }
 
 static void print_kernel_ident(void)
 {
     printk("%s %.*s %s\n", init_utsname()->release,
         (int)strcspn(init_utsname()->version, " "),
         init_utsname()->version,
         print_tainted());
 }
 
 static int very_verbose(struct lock_class *class)
 {
 #if VERY_VERBOSE
     return class_filter(class);
 #endif
     return 0;
 }
 
 /*
  * Is this the address of a static object:
  */
 #ifdef __KERNEL__
 /*
  * Check if an address is part of freed initmem. After initmem is freed,
  * memory can be allocated from it, and such allocations would then have
  * addresses within the range [_stext, _end].
  */
 #ifndef arch_is_kernel_initmem_freed
 static int arch_is_kernel_initmem_freed(unsigned long addr)
 {
     if (system_state < SYSTEM_FREEING_INITMEM)
         return 0;
 
     return init_section_contains((void *)addr, 1);
 }
 #endif
 
 static int static_obj(const void *obj)
 {
     unsigned long start = (unsigned long) &_stext,
               end   = (unsigned long) &_end,
               addr  = (unsigned long) obj;
 
     if (arch_is_kernel_initmem_freed(addr))
         return 0;
 
     /*
      * static variable?
      */
     if ((addr >= start) && (addr < end))
         return 1;
 
     /*
      * in-kernel percpu var?
      */
     if (is_kernel_percpu_address(addr))
         return 1;
 
     /*
      * module static or percpu var?
      */
     return is_module_address(addr) || is_module_percpu_address(addr);
 }
 #endif
 
 /*
  * To make lock name printouts unique, we calculate a unique
  * class->name_version generation counter. The caller must hold the graph
  * lock.
  */
 static int count_matching_names(struct lock_class *new_class)
 {
     struct lock_class *class;
     int count = 0;
 
     if (!new_class->name)
         return 0;
 
     list_for_each_entry(class, &all_lock_classes, lock_entry) {
         if (new_class->key - new_class->subclass == class->key)
             return class->name_version;
         if (class->name && !strcmp(class->name, new_class->name))
             count = max(count, class->name_version);
     }
 
     return count + 1;
 }
 
 /* used from NMI context -- must be lockless */
 static noinstr struct lock_class *
 look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
 {
     struct lockdep_subclass_key *key;
     struct hlist_head *hash_head;
     struct lock_class *class;
 
     if (unlikely(subclass >= MAX_LOCKDEP_SUBCLASSES)) {
         instrumentation_begin();
         debug_locks_off();
         printk(KERN_ERR
             "BUG: looking up invalid subclass: %u\n", subclass);
         printk(KERN_ERR
             "turning off the locking correctness validator.\n");
         dump_stack();
         instrumentation_end();
         return NULL;
     }
 
     /*
      * If it is not initialised then it has never been locked,
      * so it won't be present in the hash table.
      */
     if (unlikely(!lock->key))
         return NULL;
 
     /*
      * NOTE: the class-key must be unique. For dynamic locks, a static
      * lock_class_key variable is passed in through the mutex_init()
      * (or spin_lock_init()) call - which acts as the key. For static
      * locks we use the lock object itself as the key.
      */
     BUILD_BUG_ON(sizeof(struct lock_class_key) >
             sizeof(struct lockdep_map));
 
     key = lock->key->subkeys + subclass;
 
     hash_head = classhashentry(key);
 
     /*
      * We do an RCU walk of the hash, see lockdep_free_key_range().
      */
     if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
         return NULL;
 
     hlist_for_each_entry_rcu_notrace(class, hash_head, hash_entry) {
         if (class->key == key) {
             /*
              * Huh! same key, different name? Did someone trample
              * on some memory? We're most confused.
              */
             WARN_ON_ONCE(class->name != lock->name &&
                      lock->key != &__lockdep_no_validate__);
             return class;
         }
     }
 
     return NULL;
 }
 
 /*
  * Static locks do not have their class-keys yet - for them the key is
  * the lock object itself. If the lock is in the per cpu area, the
  * canonical address of the lock (per cpu offset removed) is used.
  */
 static bool assign_lock_key(struct lockdep_map *lock)
 {
     unsigned long can_addr, addr = (unsigned long)lock;
 
 #ifdef __KERNEL__
     /*
      * lockdep_free_key_range() assumes that struct lock_class_key
      * objects do not overlap. Since we use the address of lock
      * objects as class key for static objects, check whether the
      * size of lock_class_key objects does not exceed the size of
      * the smallest lock object.
      */
     BUILD_BUG_ON(sizeof(struct lock_class_key) > sizeof(raw_spinlock_t));
 #endif
 
     if (__is_kernel_percpu_address(addr, &can_addr))
         lock->key = (void *)can_addr;
     else if (__is_module_percpu_address(addr, &can_addr))
         lock->key = (void *)can_addr;
     else if (static_obj(lock))
         lock->key = (void *)lock;
     else {
         /* Debug-check: all keys must be persistent! */
         debug_locks_off();
         pr_err("INFO: trying to register non-static key.\n");
         pr_err("The code is fine but needs lockdep annotation, or maybe\n");
         pr_err("you didn't initialize this object before use?\n");
         pr_err("turning off the locking correctness validator.\n");
         dump_stack();
         return false;
     }
 
     return true;
 }
 
 #ifdef CONFIG_DEBUG_LOCKDEP
 
 /* Check whether element @e occurs in list @h */
 static bool in_list(struct list_head *e, struct list_head *h)
 {
     struct list_head *f;
 
     list_for_each(f, h) {
         if (e == f)
             return true;
     }
 
     return false;
 }
 
 /*
  * Check whether entry @e occurs in any of the locks_after or locks_before
  * lists.
  */
 static bool in_any_class_list(struct list_head *e)
 {
     struct lock_class *class;
     int i;
 
     for (i = 0; i < ARRAY_SIZE(lock_classes); i++) {
         class = &lock_classes[i];
         if (in_list(e, &class->locks_after) ||
             in_list(e, &class->locks_before))
             return true;
     }
     return false;
 }
 
 static bool class_lock_list_valid(struct lock_class *c, struct list_head *h)
 {
     struct lock_list *e;
 
     list_for_each_entry(e, h, entry) {
         if (e->links_to != c) {
             printk(KERN_INFO "class %s: mismatch for lock entry %ld; class %s <> %s",
                    c->name ? : "(?)",
                    (unsigned long)(e - list_entries),
                    e->links_to && e->links_to->name ?
                    e->links_to->name : "(?)",
                    e->class && e->class->name ? e->class->name :
                    "(?)");
             return false;
         }
     }
     return true;
 }
 
 #ifdef CONFIG_PROVE_LOCKING
 static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
 #endif
 
 static bool check_lock_chain_key(struct lock_chain *chain)
 {
 #ifdef CONFIG_PROVE_LOCKING
     u64 chain_key = INITIAL_CHAIN_KEY;
     int i;
 
     for (i = chain->base; i < chain->base + chain->depth; i++)
         chain_key = iterate_chain_key(chain_key, chain_hlocks[i]);
     /*
      * The 'unsigned long long' casts avoid that a compiler warning
      * is reported when building tools/lib/lockdep.
      */
     if (chain->chain_key != chain_key) {
         printk(KERN_INFO "chain %lld: key %#llx <> %#llx\n",
                (unsigned long long)(chain - lock_chains),
                (unsigned long long)chain->chain_key,
                (unsigned long long)chain_key);
         return false;
     }
 #endif
     return true;
 }
 
 static bool in_any_zapped_class_list(struct lock_class *class)
 {
     struct pending_free *pf;
     int i;
 
     for (i = 0, pf = delayed_free.pf; i < ARRAY_SIZE(delayed_free.pf); i++, pf++) {
         if (in_list(&class->lock_entry, &pf->zapped))
             return true;
     }
 
     return false;
 }
 
 static bool __check_data_structures(void)
 {
     struct lock_class *class;
     struct lock_chain *chain;
     struct hlist_head *head;
     struct lock_list *e;
     int i;
 
     /* Check whether all classes occur in a lock list. */
     for (i = 0; i < ARRAY_SIZE(lock_classes); i++) {
         class = &lock_classes[i];
         if (!in_list(&class->lock_entry, &all_lock_classes) &&
             !in_list(&class->lock_entry, &free_lock_classes) &&
             !in_any_zapped_class_list(class)) {
             printk(KERN_INFO "class %px/%s is not in any class list\n",
                    class, class->name ? : "(?)");
             return false;
         }
     }
 
     /* Check whether all classes have valid lock lists. */
     for (i = 0; i < ARRAY_SIZE(lock_classes); i++) {
         class = &lock_classes[i];
         if (!class_lock_list_valid(class, &class->locks_before))
             return false;
         if (!class_lock_list_valid(class, &class->locks_after))
             return false;
     }
 
     /* Check the chain_key of all lock chains. */
     for (i = 0; i < ARRAY_SIZE(chainhash_table); i++) {
         head = chainhash_table + i;
         hlist_for_each_entry_rcu(chain, head, entry) {
             if (!check_lock_chain_key(chain))
                 return false;
         }
     }
 
     /*
      * Check whether all list entries that are in use occur in a class
      * lock list.
      */
     for_each_set_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) {
         e = list_entries + i;
         if (!in_any_class_list(&e->entry)) {
             printk(KERN_INFO "list entry %d is not in any class list; class %s <> %s\n",
                    (unsigned int)(e - list_entries),
                    e->class->name ? : "(?)",
                    e->links_to->name ? : "(?)");
             return false;
         }
     }
 
     /*
      * Check whether all list entries that are not in use do not occur in
      * a class lock list.
      */
     for_each_clear_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) {
         e = list_entries + i;
         if (in_any_class_list(&e->entry)) {
             printk(KERN_INFO "list entry %d occurs in a class list; class %s <> %s\n",
                    (unsigned int)(e - list_entries),
                    e->class && e->class->name ? e->class->name :
                    "(?)",
                    e->links_to && e->links_to->name ?
                    e->links_to->name : "(?)");
             return false;
         }
     }
 
     return true;
 }
 
 int check_consistency = 0;
 module_param(check_consistency, int, 0644);
 
 static void check_data_structures(void)
 {
     static bool once = false;
 
     if (check_consistency && !once) {
         if (!__check_data_structures()) {
             once = true;
             WARN_ON(once);
         }
     }
 }
 
 #else /* CONFIG_DEBUG_LOCKDEP */
 
 static inline void check_data_structures(void) { }
 
 #endif /* CONFIG_DEBUG_LOCKDEP */
 
 static void init_chain_block_buckets(void);
 
 /*
  * Initialize the lock_classes[] array elements, the free_lock_classes list
  * and also the delayed_free structure.
  */
 static void init_data_structures_once(void)
 {
     static bool __read_mostly ds_initialized, rcu_head_initialized;
     int i;
 
     if (likely(rcu_head_initialized))
         return;
 
     if (system_state >= SYSTEM_SCHEDULING) {
         init_rcu_head(&delayed_free.rcu_head);
         rcu_head_initialized = true;
     }
 
     if (ds_initialized)
         return;
 
     ds_initialized = true;
 
     INIT_LIST_HEAD(&delayed_free.pf[0].zapped);
     INIT_LIST_HEAD(&delayed_free.pf[1].zapped);
 
     for (i = 0; i < ARRAY_SIZE(lock_classes); i++) {
         list_add_tail(&lock_classes[i].lock_entry, &free_lock_classes);
         INIT_LIST_HEAD(&lock_classes[i].locks_after);
         INIT_LIST_HEAD(&lock_classes[i].locks_before);
     }
     init_chain_block_buckets();
 }
 
 static inline struct hlist_head *keyhashentry(const struct lock_class_key *key)
 {
     unsigned long hash = hash_long((uintptr_t)key, KEYHASH_BITS);
 
     return lock_keys_hash + hash;
 }
 
 /* Register a dynamically allocated key. */
 void lockdep_register_key(struct lock_class_key *key)
 {
     struct hlist_head *hash_head;
     struct lock_class_key *k;
     unsigned long flags;
 
     if (WARN_ON_ONCE(static_obj(key)))
         return;
     hash_head = keyhashentry(key);
 
     raw_local_irq_save(flags);
     if (!graph_lock())
         goto restore_irqs;
     hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
         if (WARN_ON_ONCE(k == key))
             goto out_unlock;
     }
     hlist_add_head_rcu(&key->hash_entry, hash_head);
 out_unlock:
     graph_unlock();
 restore_irqs:
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lockdep_register_key);
 
 /* Check whether a key has been registered as a dynamic key. */
 static bool is_dynamic_key(const struct lock_class_key *key)
 {
     struct hlist_head *hash_head;
     struct lock_class_key *k;
     bool found = false;
 
     if (WARN_ON_ONCE(static_obj(key)))
         return false;
 
     /*
      * If lock debugging is disabled lock_keys_hash[] may contain
      * pointers to memory that has already been freed. Avoid triggering
      * a use-after-free in that case by returning early.
      */
     if (!debug_locks)
         return true;
 
     hash_head = keyhashentry(key);
 
     rcu_read_lock();
     hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
         if (k == key) {
             found = true;
             break;
         }
     }
     rcu_read_unlock();
 
     return found;
 }
 
 /*
  * Register a lock's class in the hash-table, if the class is not present
  * yet. Otherwise we look it up. We cache the result in the lock object
  * itself, so actual lookup of the hash should be once per lock object.
  */
 static struct lock_class *
 register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
 {
     struct lockdep_subclass_key *key;
     struct hlist_head *hash_head;
     struct lock_class *class;
     int idx;
 
     DEBUG_LOCKS_WARN_ON(!irqs_disabled());
 
     class = look_up_lock_class(lock, subclass);
     if (likely(class))
         goto out_set_class_cache;
 
     if (!lock->key) {
         if (!assign_lock_key(lock))
             return NULL;
     } else if (!static_obj(lock->key) && !is_dynamic_key(lock->key)) {
         return NULL;
     }
 
     key = lock->key->subkeys + subclass;
     hash_head = classhashentry(key);
 
     if (!graph_lock()) {
         return NULL;
     }
     /*
      * We have to do the hash-walk again, to avoid races
      * with another CPU:
      */
     hlist_for_each_entry_rcu(class, hash_head, hash_entry) {
         if (class->key == key)
             goto out_unlock_set;
     }
 
     init_data_structures_once();
 
     /* Allocate a new lock class and add it to the hash. */
     class = list_first_entry_or_null(&free_lock_classes, typeof(*class),
                      lock_entry);
     if (!class) {
         if (!debug_locks_off_graph_unlock()) {
             return NULL;
         }
 
         print_lockdep_off("BUG: MAX_LOCKDEP_KEYS too low!");
         dump_stack();
         return NULL;
     }
     nr_lock_classes++;
     __set_bit(class - lock_classes, lock_classes_in_use);
     debug_atomic_inc(nr_unused_locks);
     class->key = key;
     class->name = lock->name;
     class->subclass = subclass;
     WARN_ON_ONCE(!list_empty(&class->locks_before));
     WARN_ON_ONCE(!list_empty(&class->locks_after));
     class->name_version = count_matching_names(class);
     class->wait_type_inner = lock->wait_type_inner;
     class->wait_type_outer = lock->wait_type_outer;
     class->lock_type = lock->lock_type;
     /*
      * We use RCU's safe list-add method to make
      * parallel walking of the hash-list safe:
      */
     hlist_add_head_rcu(&class->hash_entry, hash_head);
     /*
      * Remove the class from the free list and add it to the global list
      * of classes.
      */
     list_move_tail(&class->lock_entry, &all_lock_classes);
     idx = class - lock_classes;
     if (idx > max_lock_class_idx)
         max_lock_class_idx = idx;
 
     if (verbose(class)) {
         graph_unlock();
 
         printk("\nnew class %px: %s", class->key, class->name);
         if (class->name_version > 1)
             printk(KERN_CONT "#%d", class->name_version);
         printk(KERN_CONT "\n");
         dump_stack();
 
         if (!graph_lock()) {
             return NULL;
         }
     }
 out_unlock_set:
     graph_unlock();
 
 out_set_class_cache:
     if (!subclass || force)
         lock->class_cache[0] = class;
     else if (subclass < NR_LOCKDEP_CACHING_CLASSES)
         lock->class_cache[subclass] = class;
 
     /*
      * Hash collision, did we smoke some? We found a class with a matching
      * hash but the subclass -- which is hashed in -- didn't match.
      */
     if (DEBUG_LOCKS_WARN_ON(class->subclass != subclass))
         return NULL;
 
     return class;
 }
 
 #ifdef CONFIG_PROVE_LOCKING
 /*
  * Allocate a lockdep entry. (assumes the graph_lock held, returns
  * with NULL on failure)
  */
 static struct lock_list *alloc_list_entry(void)
 {
     int idx = find_first_zero_bit(list_entries_in_use,
                       ARRAY_SIZE(list_entries));
 
     if (idx >= ARRAY_SIZE(list_entries)) {
         if (!debug_locks_off_graph_unlock())
             return NULL;
 
         print_lockdep_off("BUG: MAX_LOCKDEP_ENTRIES too low!");
         dump_stack();
         return NULL;
     }
     nr_list_entries++;
     __set_bit(idx, list_entries_in_use);
     return list_entries + idx;
 }
 
 /*
  * Add a new dependency to the head of the list:
  */
 static int add_lock_to_list(struct lock_class *this,
                 struct lock_class *links_to, struct list_head *head,
                 u16 distance, u8 dep,
                 const struct lock_trace *trace)
 {
     struct lock_list *entry;
     /*
      * Lock not present yet - get a new dependency struct and
      * add it to the list:
      */
     entry = alloc_list_entry();
     if (!entry)
         return 0;
 
     entry->class = this;
     entry->links_to = links_to;
     entry->dep = dep;
     entry->distance = distance;
     entry->trace = trace;
     /*
      * Both allocation and removal are done under the graph lock; but
      * iteration is under RCU-sched; see look_up_lock_class() and
      * lockdep_free_key_range().
      */
     list_add_tail_rcu(&entry->entry, head);
 
     return 1;
 }
 
 /*
  * For good efficiency of modular, we use power of 2
  */
 #define MAX_CIRCULAR_QUEUE_SIZE     (1UL << CONFIG_LOCKDEP_CIRCULAR_QUEUE_BITS)
 #define CQ_MASK             (MAX_CIRCULAR_QUEUE_SIZE-1)
 
 /*
  * The circular_queue and helpers are used to implement graph
  * breadth-first search (BFS) algorithm, by which we can determine
  * whether there is a path from a lock to another. In deadlock checks,
  * a path from the next lock to be acquired to a previous held lock
  * indicates that adding the <prev> -> <next> lock dependency will
  * produce a circle in the graph. Breadth-first search instead of
  * depth-first search is used in order to find the shortest (circular)
  * path.
  */
 struct circular_queue {
     struct lock_list *element[MAX_CIRCULAR_QUEUE_SIZE];
     unsigned int  front, rear;
 };
 
 static struct circular_queue lock_cq;
 
 unsigned int max_bfs_queue_depth;
 
 static unsigned int lockdep_dependency_gen_id;
 
 static inline void __cq_init(struct circular_queue *cq)
 {
     cq->front = cq->rear = 0;
     lockdep_dependency_gen_id++;
 }
 
 static inline int __cq_empty(struct circular_queue *cq)
 {
     return (cq->front == cq->rear);
 }
 
 static inline int __cq_full(struct circular_queue *cq)
 {
     return ((cq->rear + 1) & CQ_MASK) == cq->front;
 }
 
 static inline int __cq_enqueue(struct circular_queue *cq, struct lock_list *elem)
 {
     if (__cq_full(cq))
         return -1;
 
     cq->element[cq->rear] = elem;
     cq->rear = (cq->rear + 1) & CQ_MASK;
     return 0;
 }
 
 /*
  * Dequeue an element from the circular_queue, return a lock_list if
  * the queue is not empty, or NULL if otherwise.
  */
 static inline struct lock_list * __cq_dequeue(struct circular_queue *cq)
 {
     struct lock_list * lock;
 
     if (__cq_empty(cq))
         return NULL;
 
     lock = cq->element[cq->front];
     cq->front = (cq->front + 1) & CQ_MASK;
 
     return lock;
 }
 
 static inline unsigned int  __cq_get_elem_count(struct circular_queue *cq)
 {
     return (cq->rear - cq->front) & CQ_MASK;
 }
 
 static inline void mark_lock_accessed(struct lock_list *lock)
 {
     lock->class->dep_gen_id = lockdep_dependency_gen_id;
 }
 
 static inline void visit_lock_entry(struct lock_list *lock,
                     struct lock_list *parent)
 {
     lock->parent = parent;
 }
 
 static inline unsigned long lock_accessed(struct lock_list *lock)
 {
     return lock->class->dep_gen_id == lockdep_dependency_gen_id;
 }
 
 static inline struct lock_list *get_lock_parent(struct lock_list *child)
 {
     return child->parent;
 }
 
 static inline int get_lock_depth(struct lock_list *child)
 {
     int depth = 0;
     struct lock_list *parent;
 
     while ((parent = get_lock_parent(child))) {
         child = parent;
         depth++;
     }
     return depth;
 }
 
 /*
  * Return the forward or backward dependency list.
  *
  * @lock:   the lock_list to get its class's dependency list
  * @offset: the offset to struct lock_class to determine whether it is
  *          locks_after or locks_before
  */
 static inline struct list_head *get_dep_list(struct lock_list *lock, int offset)
 {
     void *lock_class = lock->class;
 
     return lock_class + offset;
 }
 /*
  * Return values of a bfs search:
  *
  * BFS_E* indicates an error
  * BFS_R* indicates a result (match or not)
  *
  * BFS_EINVALIDNODE: Find a invalid node in the graph.
  *
  * BFS_EQUEUEFULL: The queue is full while doing the bfs.
  *
  * BFS_RMATCH: Find the matched node in the graph, and put that node into
  *             *@target_entry.
  *
  * BFS_RNOMATCH: Haven't found the matched node and keep *@target_entry
  *               _unchanged_.
  */
 enum bfs_result {
     BFS_EINVALIDNODE = -2,
     BFS_EQUEUEFULL = -1,
     BFS_RMATCH = 0,
     BFS_RNOMATCH = 1,
 };
 
 /*
  * bfs_result < 0 means error
  */
 static inline bool bfs_error(enum bfs_result res)
 {
     return res < 0;
 }
 
 /*
  * DEP_*_BIT in lock_list::dep
  *
  * For dependency @prev -> @next:
  *
  *   SR: @prev is shared reader (->read != 0) and @next is recursive reader
  *       (->read == 2)
  *   ER: @prev is exclusive locker (->read == 0) and @next is recursive reader
  *   SN: @prev is shared reader and @next is non-recursive locker (->read != 2)
  *   EN: @prev is exclusive locker and @next is non-recursive locker
  *
  * Note that we define the value of DEP_*_BITs so that:
  *   bit0 is prev->read == 0
  *   bit1 is next->read != 2
  */
 #define DEP_SR_BIT (0 + (0 << 1)) /* 0 */
 #define DEP_ER_BIT (1 + (0 << 1)) /* 1 */
 #define DEP_SN_BIT (0 + (1 << 1)) /* 2 */
 #define DEP_EN_BIT (1 + (1 << 1)) /* 3 */
 
 #define DEP_SR_MASK (1U << (DEP_SR_BIT))
 #define DEP_ER_MASK (1U << (DEP_ER_BIT))
 #define DEP_SN_MASK (1U << (DEP_SN_BIT))
 #define DEP_EN_MASK (1U << (DEP_EN_BIT))
 
 static inline unsigned int
 __calc_dep_bit(struct held_lock *prev, struct held_lock *next)
 {
     return (prev->read == 0) + ((next->read != 2) << 1);
 }
 
 static inline u8 calc_dep(struct held_lock *prev, struct held_lock *next)
 {
     return 1U << __calc_dep_bit(prev, next);
 }
 
 /*
  * calculate the dep_bit for backwards edges. We care about whether @prev is
  * shared and whether @next is recursive.
  */
 static inline unsigned int
 __calc_dep_bitb(struct held_lock *prev, struct held_lock *next)
 {
     return (next->read != 2) + ((prev->read == 0) << 1);
 }
 
 static inline u8 calc_depb(struct held_lock *prev, struct held_lock *next)
 {
     return 1U << __calc_dep_bitb(prev, next);
 }
 
 /*
  * Initialize a lock_list entry @lock belonging to @class as the root for a BFS
  * search.
  */
 static inline void __bfs_init_root(struct lock_list *lock,
                    struct lock_class *class)
 {
     lock->class = class;
     lock->parent = NULL;
     lock->only_xr = 0;
 }
 
 /*
  * Initialize a lock_list entry @lock based on a lock acquisition @hlock as the
  * root for a BFS search.
  *
  * ->only_xr of the initial lock node is set to @hlock->read == 2, to make sure
  * that <prev> -> @hlock and @hlock -> <whatever __bfs() found> is not -(*R)->
  * and -(S*)->.
  */
 static inline void bfs_init_root(struct lock_list *lock,
                  struct held_lock *hlock)
 {
     __bfs_init_root(lock, hlock_class(hlock));
     lock->only_xr = (hlock->read == 2);
 }
 
 /*
  * Similar to bfs_init_root() but initialize the root for backwards BFS.
  *
  * ->only_xr of the initial lock node is set to @hlock->read != 0, to make sure
  * that <next> -> @hlock and @hlock -> <whatever backwards BFS found> is not
  * -(*S)-> and -(R*)-> (reverse order of -(*R)-> and -(S*)->).
  */
 static inline void bfs_init_rootb(struct lock_list *lock,
                   struct held_lock *hlock)
 {
     __bfs_init_root(lock, hlock_class(hlock));
     lock->only_xr = (hlock->read != 0);
 }
 
 static inline struct lock_list *__bfs_next(struct lock_list *lock, int offset)
 {
     if (!lock || !lock->parent)
         return NULL;
 
     return list_next_or_null_rcu(get_dep_list(lock->parent, offset),
                      &lock->entry, struct lock_list, entry);
 }
 
 /*
  * Breadth-First Search to find a strong path in the dependency graph.
  *
  * @source_entry: the source of the path we are searching for.
  * @data: data used for the second parameter of @match function
  * @match: match function for the search
  * @target_entry: pointer to the target of a matched path
  * @offset: the offset to struct lock_class to determine whether it is
  *          locks_after or locks_before
  *
  * We may have multiple edges (considering different kinds of dependencies,
  * e.g. ER and SN) between two nodes in the dependency graph. But
  * only the strong dependency path in the graph is relevant to deadlocks. A
  * strong dependency path is a dependency path that doesn't have two adjacent
  * dependencies as -(*R)-> -(S*)->, please see:
  *
  *         Documentation/locking/lockdep-design.rst
  *
  * for more explanation of the definition of strong dependency paths
  *
  * In __bfs(), we only traverse in the strong dependency path:
  *
  *     In lock_list::only_xr, we record whether the previous dependency only
  *     has -(*R)-> in the search, and if it does (prev only has -(*R)->), we
  *     filter out any -(S*)-> in the current dependency and after that, the
  *     ->only_xr is set according to whether we only have -(*R)-> left.
  */
 static enum bfs_result __bfs(struct lock_list *source_entry,
                  void *data,
                  bool (*match)(struct lock_list *entry, void *data),
                  bool (*skip)(struct lock_list *entry, void *data),
                  struct lock_list **target_entry,
                  int offset)
 {
     struct circular_queue *cq = &lock_cq;
     struct lock_list *lock = NULL;
     struct lock_list *entry;
     struct list_head *head;
     unsigned int cq_depth;
     bool first;
 
     lockdep_assert_locked();
 
     __cq_init(cq);
     __cq_enqueue(cq, source_entry);
 
     while ((lock = __bfs_next(lock, offset)) || (lock = __cq_dequeue(cq))) {
         if (!lock->class)
             return BFS_EINVALIDNODE;
 
         /*
          * Step 1: check whether we already finish on this one.
          *
          * If we have visited all the dependencies from this @lock to
          * others (iow, if we have visited all lock_list entries in
          * @lock->class->locks_{after,before}) we skip, otherwise go
          * and visit all the dependencies in the list and mark this
          * list accessed.
          */
         if (lock_accessed(lock))
             continue;
         else
             mark_lock_accessed(lock);
 
         /*
          * Step 2: check whether prev dependency and this form a strong
          *         dependency path.
          */
         if (lock->parent) { /* Parent exists, check prev dependency */
             u8 dep = lock->dep;
             bool prev_only_xr = lock->parent->only_xr;
 
             /*
              * Mask out all -(S*)-> if we only have *R in previous
              * step, because -(*R)-> -(S*)-> don't make up a strong
              * dependency.
              */
             if (prev_only_xr)
                 dep &= ~(DEP_SR_MASK | DEP_SN_MASK);
 
             /* If nothing left, we skip */
             if (!dep)
                 continue;
 
             /* If there are only -(*R)-> left, set that for the next step */
             lock->only_xr = !(dep & (DEP_SN_MASK | DEP_EN_MASK));
         }
 
         /*
          * Step 3: we haven't visited this and there is a strong
          *         dependency path to this, so check with @match.
          *         If @skip is provide and returns true, we skip this
          *         lock (and any path this lock is in).
          */
         if (skip && skip(lock, data))
             continue;
 
         if (match(lock, data)) {
             *target_entry = lock;
             return BFS_RMATCH;
         }
 
         /*
          * Step 4: if not match, expand the path by adding the
          *         forward or backwards dependencies in the search
          *
          */
         first = true;
         head = get_dep_list(lock, offset);
         list_for_each_entry_rcu(entry, head, entry) {
             visit_lock_entry(entry, lock);
 
             /*
              * Note we only enqueue the first of the list into the
              * queue, because we can always find a sibling
              * dependency from one (see __bfs_next()), as a result
              * the space of queue is saved.
              */
             if (!first)
                 continue;
 
             first = false;
 
             if (__cq_enqueue(cq, entry))
                 return BFS_EQUEUEFULL;
 
             cq_depth = __cq_get_elem_count(cq);
             if (max_bfs_queue_depth < cq_depth)
                 max_bfs_queue_depth = cq_depth;
         }
     }
 
     return BFS_RNOMATCH;
 }
 
 static inline enum bfs_result
 __bfs_forwards(struct lock_list *src_entry,
            void *data,
            bool (*match)(struct lock_list *entry, void *data),
            bool (*skip)(struct lock_list *entry, void *data),
            struct lock_list **target_entry)
 {
     return __bfs(src_entry, data, match, skip, target_entry,
              offsetof(struct lock_class, locks_after));
 
 }
 
 static inline enum bfs_result
 __bfs_backwards(struct lock_list *src_entry,
         void *data,
         bool (*match)(struct lock_list *entry, void *data),
            bool (*skip)(struct lock_list *entry, void *data),
         struct lock_list **target_entry)
 {
     return __bfs(src_entry, data, match, skip, target_entry,
              offsetof(struct lock_class, locks_before));
 
 }
 
 static void print_lock_trace(const struct lock_trace *trace,
                  unsigned int spaces)
 {
     stack_trace_print(trace->entries, trace->nr_entries, spaces);
 }
 
 /*
  * Print a dependency chain entry (this is only done when a deadlock
  * has been detected):
  */
 static noinline void
 print_circular_bug_entry(struct lock_list *target, int depth)
 {
     if (debug_locks_silent)
         return;
     printk("\n-> #%u", depth);
     print_lock_name(target->class);
     printk(KERN_CONT ":\n");
     print_lock_trace(target->trace, 6);
 }
 
 static void
 print_circular_lock_scenario(struct held_lock *src,
                  struct held_lock *tgt,
                  struct lock_list *prt)
 {
     struct lock_class *source = hlock_class(src);
     struct lock_class *target = hlock_class(tgt);
     struct lock_class *parent = prt->class;
 
     /*
      * A direct locking problem where unsafe_class lock is taken
      * directly by safe_class lock, then all we need to show
      * is the deadlock scenario, as it is obvious that the
      * unsafe lock is taken under the safe lock.
      *
      * But if there is a chain instead, where the safe lock takes
      * an intermediate lock (middle_class) where this lock is
      * not the same as the safe lock, then the lock chain is
      * used to describe the problem. Otherwise we would need
      * to show a different CPU case for each link in the chain
      * from the safe_class lock to the unsafe_class lock.
      */
     if (parent != source) {
         printk("Chain exists of:\n  ");
         __print_lock_name(source);
         printk(KERN_CONT " --> ");
         __print_lock_name(parent);
         printk(KERN_CONT " --> ");
         __print_lock_name(target);
         printk(KERN_CONT "\n\n");
     }
 
     printk(" Possible unsafe locking scenario:\n\n");
     printk("       CPU0                    CPU1\n");
     printk("       ----                    ----\n");
     printk("  lock(");
     __print_lock_name(target);
     printk(KERN_CONT ");\n");
     printk("                               lock(");
     __print_lock_name(parent);
     printk(KERN_CONT ");\n");
     printk("                               lock(");
     __print_lock_name(target);
     printk(KERN_CONT ");\n");
     printk("  lock(");
     __print_lock_name(source);
     printk(KERN_CONT ");\n");
     printk("\n *** DEADLOCK ***\n\n");
 }
 
 /*
  * When a circular dependency is detected, print the
  * header first:
  */
 static noinline void
 print_circular_bug_header(struct lock_list *entry, unsigned int depth,
             struct held_lock *check_src,
             struct held_lock *check_tgt)
 {
     struct task_struct *curr = current;
 
     if (debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("======================================================\n");
     pr_warn("WARNING: possible circular locking dependency detected\n");
     print_kernel_ident();
     pr_warn("------------------------------------------------------\n");
     pr_warn("%s/%d is trying to acquire lock:\n",
         curr->comm, task_pid_nr(curr));
     print_lock(check_src);
 
     pr_warn("\nbut task is already holding lock:\n");
 
     print_lock(check_tgt);
     pr_warn("\nwhich lock already depends on the new lock.\n\n");
     pr_warn("\nthe existing dependency chain (in reverse order) is:\n");
 
     print_circular_bug_entry(entry, depth);
 }
 
 /*
  * We are about to add A -> B into the dependency graph, and in __bfs() a
  * strong dependency path A -> .. -> B is found: hlock_class equals
  * entry->class.
  *
  * If A -> .. -> B can replace A -> B in any __bfs() search (means the former
  * is _stronger_ than or equal to the latter), we consider A -> B as redundant.
  * For example if A -> .. -> B is -(EN)-> (i.e. A -(E*)-> .. -(*N)-> B), and A
  * -> B is -(ER)-> or -(EN)->, then we don't need to add A -> B into the
  * dependency graph, as any strong path ..-> A -> B ->.. we can get with
  * having dependency A -> B, we could already get a equivalent path ..-> A ->
  * .. -> B -> .. with A -> .. -> B. Therefore A -> B is redundant.
  *
  * We need to make sure both the start and the end of A -> .. -> B is not
  * weaker than A -> B. For the start part, please see the comment in
  * check_redundant(). For the end part, we need:
  *
  * Either
  *
  *     a) A -> B is -(*R)-> (everything is not weaker than that)
  *
  * or
  *
  *     b) A -> .. -> B is -(*N)-> (nothing is stronger than this)
  *
  */
 static inline bool hlock_equal(struct lock_list *entry, void *data)
 {
     struct held_lock *hlock = (struct held_lock *)data;
 
     return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */
            (hlock->read == 2 ||  /* A -> B is -(*R)-> */
         !entry->only_xr); /* A -> .. -> B is -(*N)-> */
 }
 
 /*
  * We are about to add B -> A into the dependency graph, and in __bfs() a
  * strong dependency path A -> .. -> B is found: hlock_class equals
  * entry->class.
  *
  * We will have a deadlock case (conflict) if A -> .. -> B -> A is a strong
  * dependency cycle, that means:
  *
  * Either
  *
  *     a) B -> A is -(E*)->
  *
  * or
  *
  *     b) A -> .. -> B is -(*N)-> (i.e. A -> .. -(*N)-> B)
  *
  * as then we don't have -(*R)-> -(S*)-> in the cycle.
  */
 static inline bool hlock_conflict(struct lock_list *entry, void *data)
 {
     struct held_lock *hlock = (struct held_lock *)data;
 
     return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */
            (hlock->read == 0 || /* B -> A is -(E*)-> */
         !entry->only_xr); /* A -> .. -> B is -(*N)-> */
 }
 
 static noinline void print_circular_bug(struct lock_list *this,
                 struct lock_list *target,
                 struct held_lock *check_src,
                 struct held_lock *check_tgt)
 {
     struct task_struct *curr = current;
     struct lock_list *parent;
     struct lock_list *first_parent;
     int depth;
 
     if (!debug_locks_off_graph_unlock() || debug_locks_silent)
         return;
 
     this->trace = save_trace();
     if (!this->trace)
         return;
 
     depth = get_lock_depth(target);
 
     print_circular_bug_header(target, depth, check_src, check_tgt);
 
     parent = get_lock_parent(target);
     first_parent = parent;
 
     while (parent) {
         print_circular_bug_entry(parent, --depth);
         parent = get_lock_parent(parent);
     }
 
     printk("\nother info that might help us debug this:\n\n");
     print_circular_lock_scenario(check_src, check_tgt,
                      first_parent);
 
     lockdep_print_held_locks(curr);
 
     printk("\nstack backtrace:\n");
     dump_stack();
 }
 
 static noinline void print_bfs_bug(int ret)
 {
     if (!debug_locks_off_graph_unlock())
         return;
 
     /*
      * Breadth-first-search failed, graph got corrupted?
      */
     WARN(1, "lockdep bfs error:%d\n", ret);
 }
 
 static bool noop_count(struct lock_list *entry, void *data)
 {
     (*(unsigned long *)data)++;
     return false;
 }
 
 static unsigned long __lockdep_count_forward_deps(struct lock_list *this)
 {
     unsigned long  count = 0;
     struct lock_list *target_entry;
 
     __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
 
     return count;
 }
 unsigned long lockdep_count_forward_deps(struct lock_class *class)
 {
     unsigned long ret, flags;
     struct lock_list this;
 
     __bfs_init_root(&this, class);
 
     raw_local_irq_save(flags);
     lockdep_lock();
     ret = __lockdep_count_forward_deps(&this);
     lockdep_unlock();
     raw_local_irq_restore(flags);
 
     return ret;
 }
 
 static unsigned long __lockdep_count_backward_deps(struct lock_list *this)
 {
     unsigned long  count = 0;
     struct lock_list *target_entry;
 
     __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
 
     return count;
 }
 
 unsigned long lockdep_count_backward_deps(struct lock_class *class)
 {
     unsigned long ret, flags;
     struct lock_list this;
 
     __bfs_init_root(&this, class);
 
     raw_local_irq_save(flags);
     lockdep_lock();
     ret = __lockdep_count_backward_deps(&this);
     lockdep_unlock();
     raw_local_irq_restore(flags);
 
     return ret;
 }
 
 /*
  * Check that the dependency graph starting at <src> can lead to
  * <target> or not.
  */
 static noinline enum bfs_result
 check_path(struct held_lock *target, struct lock_list *src_entry,
        bool (*match)(struct lock_list *entry, void *data),
        bool (*skip)(struct lock_list *entry, void *data),
        struct lock_list **target_entry)
 {
     enum bfs_result ret;
 
     ret = __bfs_forwards(src_entry, target, match, skip, target_entry);
 
     if (unlikely(bfs_error(ret)))
         print_bfs_bug(ret);
 
     return ret;
 }
 
 /*
  * Prove that the dependency graph starting at <src> can not
  * lead to <target>. If it can, there is a circle when adding
  * <target> -> <src> dependency.
  *
  * Print an error and return BFS_RMATCH if it does.
  */
 static noinline enum bfs_result
 check_noncircular(struct held_lock *src, struct held_lock *target,
           struct lock_trace **const trace)
 {
     enum bfs_result ret;
     struct lock_list *target_entry;
     struct lock_list src_entry;
 
     bfs_init_root(&src_entry, src);
 
     debug_atomic_inc(nr_cyclic_checks);
 
     ret = check_path(target, &src_entry, hlock_conflict, NULL, &target_entry);
 
     if (unlikely(ret == BFS_RMATCH)) {
         if (!*trace) {
             /*
              * If save_trace fails here, the printing might
              * trigger a WARN but because of the !nr_entries it
              * should not do bad things.
              */
             *trace = save_trace();
         }
 
         print_circular_bug(&src_entry, target_entry, src, target);
     }
 
     return ret;
 }
 
 #ifdef CONFIG_TRACE_IRQFLAGS
 
 /*
  * Forwards and backwards subgraph searching, for the purposes of
  * proving that two subgraphs can be connected by a new dependency
  * without creating any illegal irq-safe -> irq-unsafe lock dependency.
  *
  * A irq safe->unsafe deadlock happens with the following conditions:
  *
  * 1) We have a strong dependency path A -> ... -> B
  *
  * 2) and we have ENABLED_IRQ usage of B and USED_IN_IRQ usage of A, therefore
  *    irq can create a new dependency B -> A (consider the case that a holder
  *    of B gets interrupted by an irq whose handler will try to acquire A).
  *
  * 3) the dependency circle A -> ... -> B -> A we get from 1) and 2) is a
  *    strong circle:
  *
  *      For the usage bits of B:
  *        a) if A -> B is -(*N)->, then B -> A could be any type, so any
  *           ENABLED_IRQ usage suffices.
  *        b) if A -> B is -(*R)->, then B -> A must be -(E*)->, so only
  *           ENABLED_IRQ_*_READ usage suffices.
  *
  *      For the usage bits of A:
  *        c) if A -> B is -(E*)->, then B -> A could be any type, so any
  *           USED_IN_IRQ usage suffices.
  *        d) if A -> B is -(S*)->, then B -> A must be -(*N)->, so only
  *           USED_IN_IRQ_*_READ usage suffices.
  */
 
 /*
  * There is a strong dependency path in the dependency graph: A -> B, and now
  * we need to decide which usage bit of A should be accumulated to detect
  * safe->unsafe bugs.
  *
  * Note that usage_accumulate() is used in backwards search, so ->only_xr
  * stands for whether A -> B only has -(S*)-> (in this case ->only_xr is true).
  *
  * As above, if only_xr is false, which means A -> B has -(E*)-> dependency
  * path, any usage of A should be considered. Otherwise, we should only
  * consider _READ usage.
  */
 static inline bool usage_accumulate(struct lock_list *entry, void *mask)
 {
     if (!entry->only_xr)
         *(unsigned long *)mask |= entry->class->usage_mask;
     else /* Mask out _READ usage bits */
         *(unsigned long *)mask |= (entry->class->usage_mask & LOCKF_IRQ);
 
     return false;
 }
 
 /*
  * There is a strong dependency path in the dependency graph: A -> B, and now
  * we need to decide which usage bit of B conflicts with the usage bits of A,
  * i.e. which usage bit of B may introduce safe->unsafe deadlocks.
  *
  * As above, if only_xr is false, which means A -> B has -(*N)-> dependency
  * path, any usage of B should be considered. Otherwise, we should only
  * consider _READ usage.
  */
 static inline bool usage_match(struct lock_list *entry, void *mask)
 {
     if (!entry->only_xr)
         return !!(entry->class->usage_mask & *(unsigned long *)mask);
     else /* Mask out _READ usage bits */
         return !!((entry->class->usage_mask & LOCKF_IRQ) & *(unsigned long *)mask);
 }
 
 static inline bool usage_skip(struct lock_list *entry, void *mask)
 {
     /*
      * Skip local_lock() for irq inversion detection.
      *
      * For !RT, local_lock() is not a real lock, so it won't carry any
      * dependency.
      *
      * For RT, an irq inversion happens when we have lock A and B, and on
      * some CPU we can have:
      *
      *  lock(A);
      *  <interrupted>
      *    lock(B);
      *
      * where lock(B) cannot sleep, and we have a dependency B -> ... -> A.
      *
      * Now we prove local_lock() cannot exist in that dependency. First we
      * have the observation for any lock chain L1 -> ... -> Ln, for any
      * 1 <= i <= n, Li.inner_wait_type <= L1.inner_wait_type, otherwise
      * wait context check will complain. And since B is not a sleep lock,
      * therefore B.inner_wait_type >= 2, and since the inner_wait_type of
      * local_lock() is 3, which is greater than 2, therefore there is no
      * way the local_lock() exists in the dependency B -> ... -> A.
      *
      * As a result, we will skip local_lock(), when we search for irq
      * inversion bugs.
      */
     if (entry->class->lock_type == LD_LOCK_PERCPU) {
         if (DEBUG_LOCKS_WARN_ON(entry->class->wait_type_inner < LD_WAIT_CONFIG))
             return false;
 
         return true;
     }
 
     return false;
 }
 
 /*
  * Find a node in the forwards-direction dependency sub-graph starting
  * at @root->class that matches @bit.
  *
  * Return BFS_MATCH if such a node exists in the subgraph, and put that node
  * into *@target_entry.
  */
 static enum bfs_result
 find_usage_forwards(struct lock_list *root, unsigned long usage_mask,
             struct lock_list **target_entry)
 {
     enum bfs_result result;
 
     debug_atomic_inc(nr_find_usage_forwards_checks);
 
     result = __bfs_forwards(root, &usage_mask, usage_match, usage_skip, target_entry);
 
     return result;
 }
 
 /*
  * Find a node in the backwards-direction dependency sub-graph starting
  * at @root->class that matches @bit.
  */
 static enum bfs_result
 find_usage_backwards(struct lock_list *root, unsigned long usage_mask,
             struct lock_list **target_entry)
 {
     enum bfs_result result;
 
     debug_atomic_inc(nr_find_usage_backwards_checks);
 
     result = __bfs_backwards(root, &usage_mask, usage_match, usage_skip, target_entry);
 
     return result;
 }
 
 static void print_lock_class_header(struct lock_class *class, int depth)
 {
     int bit;
 
     printk("%*s->", depth, "");
     print_lock_name(class);
 #ifdef CONFIG_DEBUG_LOCKDEP
     printk(KERN_CONT " ops: %lu", debug_class_ops_read(class));
 #endif
     printk(KERN_CONT " {\n");
 
     for (bit = 0; bit < LOCK_TRACE_STATES; bit++) {
         if (class->usage_mask & (1 << bit)) {
             int len = depth;
 
             len += printk("%*s   %s", depth, "", usage_str[bit]);
             len += printk(KERN_CONT " at:\n");
             print_lock_trace(class->usage_traces[bit], len);
         }
     }
     printk("%*s }\n", depth, "");
 
     printk("%*s ... key      at: [<%px>] %pS\n",
         depth, "", class->key, class->key);
 }
 
 /*
  * Dependency path printing:
  *
  * After BFS we get a lock dependency path (linked via ->parent of lock_list),
  * printing out each lock in the dependency path will help on understanding how
  * the deadlock could happen. Here are some details about dependency path
  * printing:
  *
  * 1)   A lock_list can be either forwards or backwards for a lock dependency,
  *  for a lock dependency A -> B, there are two lock_lists:
  *
  *  a)  lock_list in the ->locks_after list of A, whose ->class is B and
  *      ->links_to is A. In this case, we can say the lock_list is
  *      "A -> B" (forwards case).
  *
  *  b)  lock_list in the ->locks_before list of B, whose ->class is A
  *      and ->links_to is B. In this case, we can say the lock_list is
  *      "B <- A" (bacwards case).
  *
  *  The ->trace of both a) and b) point to the call trace where B was
  *  acquired with A held.
  *
  * 2)   A "helper" lock_list is introduced during BFS, this lock_list doesn't
  *  represent a certain lock dependency, it only provides an initial entry
  *  for BFS. For example, BFS may introduce a "helper" lock_list whose
  *  ->class is A, as a result BFS will search all dependencies starting with
  *  A, e.g. A -> B or A -> C.
  *
  *  The notation of a forwards helper lock_list is like "-> A", which means
  *  we should search the forwards dependencies starting with "A", e.g A -> B
  *  or A -> C.
  *
  *  The notation of a bacwards helper lock_list is like "<- B", which means
  *  we should search the backwards dependencies ending with "B", e.g.
  *  B <- A or B <- C.
  */
 
 /*
  * printk the shortest lock dependencies from @root to @leaf in reverse order.
  *
  * We have a lock dependency path as follow:
  *
  *    @root                                                                 @leaf
  *      |                                                                     |
  *      V                                                                     V
  *            ->parent                                   ->parent
  * | lock_list | <--------- | lock_list | ... | lock_list  | <--------- | lock_list |
  * |    -> L1  |            | L1 -> L2  | ... |Ln-2 -> Ln-1|            | Ln-1 -> Ln|
  *
  * , so it's natural that we start from @leaf and print every ->class and
  * ->trace until we reach the @root.
  */
 static void __used
 print_shortest_lock_dependencies(struct lock_list *leaf,
                  struct lock_list *root)
 {
     struct lock_list *entry = leaf;
     int depth;
 
     /*compute depth from generated tree by BFS*/
     depth = get_lock_depth(leaf);
 
     do {
         print_lock_class_header(entry->class, depth);
         printk("%*s ... acquired at:\n", depth, "");
         print_lock_trace(entry->trace, 2);
         printk("\n");
 
         if (depth == 0 && (entry != root)) {
             printk("lockdep:%s bad path found in chain graph\n", __func__);
             break;
         }
 
         entry = get_lock_parent(entry);
         depth--;
     } while (entry && (depth >= 0));
 }
 
 /*
  * printk the shortest lock dependencies from @leaf to @root.
  *
  * We have a lock dependency path (from a backwards search) as follow:
  *
  *    @leaf                                                                 @root
  *      |                                                                     |
  *      V                                                                     V
  *            ->parent                                   ->parent
  * | lock_list | ---------> | lock_list | ... | lock_list  | ---------> | lock_list |
  * | L2 <- L1  |            | L3 <- L2  | ... | Ln <- Ln-1 |            |    <- Ln  |
  *
  * , so when we iterate from @leaf to @root, we actually print the lock
  * dependency path L1 -> L2 -> .. -> Ln in the non-reverse order.
  *
  * Another thing to notice here is that ->class of L2 <- L1 is L1, while the
  * ->trace of L2 <- L1 is the call trace of L2, in fact we don't have the call
  * trace of L1 in the dependency path, which is alright, because most of the
  * time we can figure out where L1 is held from the call trace of L2.
  */
 static void __used
 print_shortest_lock_dependencies_backwards(struct lock_list *leaf,
                        struct lock_list *root)
 {
     struct lock_list *entry = leaf;
     const struct lock_trace *trace = NULL;
     int depth;
 
     /*compute depth from generated tree by BFS*/
     depth = get_lock_depth(leaf);
 
     do {
         print_lock_class_header(entry->class, depth);
         if (trace) {
             printk("%*s ... acquired at:\n", depth, "");
             print_lock_trace(trace, 2);
             printk("\n");
         }
 
         /*
          * Record the pointer to the trace for the next lock_list
          * entry, see the comments for the function.
          */
         trace = entry->trace;
 
         if (depth == 0 && (entry != root)) {
             printk("lockdep:%s bad path found in chain graph\n", __func__);
             break;
         }
 
         entry = get_lock_parent(entry);
         depth--;
     } while (entry && (depth >= 0));
 }
 
 static void
 print_irq_lock_scenario(struct lock_list *safe_entry,
             struct lock_list *unsafe_entry,
             struct lock_class *prev_class,
             struct lock_class *next_class)
 {
     struct lock_class *safe_class = safe_entry->class;
     struct lock_class *unsafe_class = unsafe_entry->class;
     struct lock_class *middle_class = prev_class;
 
     if (middle_class == safe_class)
         middle_class = next_class;
 
     /*
      * A direct locking problem where unsafe_class lock is taken
      * directly by safe_class lock, then all we need to show
      * is the deadlock scenario, as it is obvious that the
      * unsafe lock is taken under the safe lock.
      *
      * But if there is a chain instead, where the safe lock takes
      * an intermediate lock (middle_class) where this lock is
      * not the same as the safe lock, then the lock chain is
      * used to describe the problem. Otherwise we would need
      * to show a different CPU case for each link in the chain
      * from the safe_class lock to the unsafe_class lock.
      */
     if (middle_class != unsafe_class) {
         printk("Chain exists of:\n  ");
         __print_lock_name(safe_class);
         printk(KERN_CONT " --> ");
         __print_lock_name(middle_class);
         printk(KERN_CONT " --> ");
         __print_lock_name(unsafe_class);
         printk(KERN_CONT "\n\n");
     }
 
     printk(" Possible interrupt unsafe locking scenario:\n\n");
     printk("       CPU0                    CPU1\n");
     printk("       ----                    ----\n");
     printk("  lock(");
     __print_lock_name(unsafe_class);
     printk(KERN_CONT ");\n");
     printk("                               local_irq_disable();\n");
     printk("                               lock(");
     __print_lock_name(safe_class);
     printk(KERN_CONT ");\n");
     printk("                               lock(");
     __print_lock_name(middle_class);
     printk(KERN_CONT ");\n");
     printk("  <Interrupt>\n");
     printk("    lock(");
     __print_lock_name(safe_class);
     printk(KERN_CONT ");\n");
     printk("\n *** DEADLOCK ***\n\n");
 }
 
 static void
 print_bad_irq_dependency(struct task_struct *curr,
              struct lock_list *prev_root,
              struct lock_list *next_root,
              struct lock_list *backwards_entry,
              struct lock_list *forwards_entry,
              struct held_lock *prev,
              struct held_lock *next,
              enum lock_usage_bit bit1,
              enum lock_usage_bit bit2,
              const char *irqclass)
 {
     if (!debug_locks_off_graph_unlock() || debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("=====================================================\n");
     pr_warn("WARNING: %s-safe -> %s-unsafe lock order detected\n",
         irqclass, irqclass);
     print_kernel_ident();
     pr_warn("-----------------------------------------------------\n");
     pr_warn("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] is trying to acquire:\n",
         curr->comm, task_pid_nr(curr),
         lockdep_hardirq_context(), hardirq_count() >> HARDIRQ_SHIFT,
         curr->softirq_context, softirq_count() >> SOFTIRQ_SHIFT,
         lockdep_hardirqs_enabled(),
         curr->softirqs_enabled);
     print_lock(next);
 
     pr_warn("\nand this task is already holding:\n");
     print_lock(prev);
     pr_warn("which would create a new lock dependency:\n");
     print_lock_name(hlock_class(prev));
     pr_cont(" ->");
     print_lock_name(hlock_class(next));
     pr_cont("\n");
 
     pr_warn("\nbut this new dependency connects a %s-irq-safe lock:\n",
         irqclass);
     print_lock_name(backwards_entry->class);
     pr_warn("\n... which became %s-irq-safe at:\n", irqclass);
 
     print_lock_trace(backwards_entry->class->usage_traces[bit1], 1);
 
     pr_warn("\nto a %s-irq-unsafe lock:\n", irqclass);
     print_lock_name(forwards_entry->class);
     pr_warn("\n... which became %s-irq-unsafe at:\n", irqclass);
     pr_warn("...");
 
     print_lock_trace(forwards_entry->class->usage_traces[bit2], 1);
 
     pr_warn("\nother info that might help us debug this:\n\n");
     print_irq_lock_scenario(backwards_entry, forwards_entry,
                 hlock_class(prev), hlock_class(next));
 
     lockdep_print_held_locks(curr);
 
     pr_warn("\nthe dependencies between %s-irq-safe lock and the holding lock:\n", irqclass);
     print_shortest_lock_dependencies_backwards(backwards_entry, prev_root);
 
     pr_warn("\nthe dependencies between the lock to be acquired");
     pr_warn(" and %s-irq-unsafe lock:\n", irqclass);
     next_root->trace = save_trace();
     if (!next_root->trace)
         return;
     print_shortest_lock_dependencies(forwards_entry, next_root);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 
 static const char *state_names[] = {
 #define LOCKDEP_STATE(__STATE) \
     __stringify(__STATE),
 #include "lockdep_states.h"
 #undef LOCKDEP_STATE
 };
 
 static const char *state_rnames[] = {
 #define LOCKDEP_STATE(__STATE) \
     __stringify(__STATE)"-READ",
 #include "lockdep_states.h"
 #undef LOCKDEP_STATE
 };
 
 static inline const char *state_name(enum lock_usage_bit bit)
 {
     if (bit & LOCK_USAGE_READ_MASK)
         return state_rnames[bit >> LOCK_USAGE_DIR_MASK];
     else
         return state_names[bit >> LOCK_USAGE_DIR_MASK];
 }
 
 /*
  * The bit number is encoded like:
  *
  *  bit0: 0 exclusive, 1 read lock
  *  bit1: 0 used in irq, 1 irq enabled
  *  bit2-n: state
  */
 static int exclusive_bit(int new_bit)
 {
     int state = new_bit & LOCK_USAGE_STATE_MASK;
     int dir = new_bit & LOCK_USAGE_DIR_MASK;
 
     /*
      * keep state, bit flip the direction and strip read.
      */
     return state | (dir ^ LOCK_USAGE_DIR_MASK);
 }
 
 /*
  * Observe that when given a bitmask where each bitnr is encoded as above, a
  * right shift of the mask transforms the individual bitnrs as -1 and
  * conversely, a left shift transforms into +1 for the individual bitnrs.
  *
  * So for all bits whose number have LOCK_ENABLED_* set (bitnr1 == 1), we can
  * create the mask with those bit numbers using LOCK_USED_IN_* (bitnr1 == 0)
  * instead by subtracting the bit number by 2, or shifting the mask right by 2.
  *
  * Similarly, bitnr1 == 0 becomes bitnr1 == 1 by adding 2, or shifting left 2.
  *
  * So split the mask (note that LOCKF_ENABLED_IRQ_ALL|LOCKF_USED_IN_IRQ_ALL is
  * all bits set) and recompose with bitnr1 flipped.
  */
 static unsigned long invert_dir_mask(unsigned long mask)
 {
     unsigned long excl = 0;
 
     /* Invert dir */
     excl |= (mask & LOCKF_ENABLED_IRQ_ALL) >> LOCK_USAGE_DIR_MASK;
     excl |= (mask & LOCKF_USED_IN_IRQ_ALL) << LOCK_USAGE_DIR_MASK;
 
     return excl;
 }
 
 /*
  * Note that a LOCK_ENABLED_IRQ_*_READ usage and a LOCK_USED_IN_IRQ_*_READ
  * usage may cause deadlock too, for example:
  *
  * P1               P2
  * <irq disabled>
  * write_lock(l1);      <irq enabled>
  *              read_lock(l2);
  * write_lock(l2);
  *              <in irq>
  *              read_lock(l1);
  *
  * , in above case, l1 will be marked as LOCK_USED_IN_IRQ_HARDIRQ_READ and l2
  * will marked as LOCK_ENABLE_IRQ_HARDIRQ_READ, and this is a possible
  * deadlock.
  *
  * In fact, all of the following cases may cause deadlocks:
  *
  *   LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*
  *   LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*
  *   LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*_READ
  *   LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*_READ
  *
  * As a result, to calculate the "exclusive mask", first we invert the
  * direction (USED_IN/ENABLED) of the original mask, and 1) for all bits with
  * bitnr0 set (LOCK_*_READ), add those with bitnr0 cleared (LOCK_*). 2) for all
  * bits with bitnr0 cleared (LOCK_*_READ), add those with bitnr0 set (LOCK_*).
  */
 static unsigned long exclusive_mask(unsigned long mask)
 {
     unsigned long excl = invert_dir_mask(mask);
 
     excl |= (excl & LOCKF_IRQ_READ) >> LOCK_USAGE_READ_MASK;
     excl |= (excl & LOCKF_IRQ) << LOCK_USAGE_READ_MASK;
 
     return excl;
 }
 
 /*
  * Retrieve the _possible_ original mask to which @mask is
  * exclusive. Ie: this is the opposite of exclusive_mask().
  * Note that 2 possible original bits can match an exclusive
  * bit: one has LOCK_USAGE_READ_MASK set, the other has it
  * cleared. So both are returned for each exclusive bit.
  */
 static unsigned long original_mask(unsigned long mask)
 {
     unsigned long excl = invert_dir_mask(mask);
 
     /* Include read in existing usages */
     excl |= (excl & LOCKF_IRQ_READ) >> LOCK_USAGE_READ_MASK;
     excl |= (excl & LOCKF_IRQ) << LOCK_USAGE_READ_MASK;
 
     return excl;
 }
 
 /*
  * Find the first pair of bit match between an original
  * usage mask and an exclusive usage mask.
  */
 static int find_exclusive_match(unsigned long mask,
                 unsigned long excl_mask,
                 enum lock_usage_bit *bitp,
                 enum lock_usage_bit *excl_bitp)
 {
     int bit, excl, excl_read;
 
     for_each_set_bit(bit, &mask, LOCK_USED) {
         /*
          * exclusive_bit() strips the read bit, however,
          * LOCK_ENABLED_IRQ_*_READ may cause deadlocks too, so we need
          * to search excl | LOCK_USAGE_READ_MASK as well.
          */
         excl = exclusive_bit(bit);
         excl_read = excl | LOCK_USAGE_READ_MASK;
         if (excl_mask & lock_flag(excl)) {
             *bitp = bit;
             *excl_bitp = excl;
             return 0;
         } else if (excl_mask & lock_flag(excl_read)) {
             *bitp = bit;
             *excl_bitp = excl_read;
             return 0;
         }
     }
     return -1;
 }
 
 /*
  * Prove that the new dependency does not connect a hardirq-safe(-read)
  * lock with a hardirq-unsafe lock - to achieve this we search
  * the backwards-subgraph starting at <prev>, and the
  * forwards-subgraph starting at <next>:
  */
 static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
                struct held_lock *next)
 {
     unsigned long usage_mask = 0, forward_mask, backward_mask;
     enum lock_usage_bit forward_bit = 0, backward_bit = 0;
     struct lock_list *target_entry1;
     struct lock_list *target_entry;
     struct lock_list this, that;
     enum bfs_result ret;
 
     /*
      * Step 1: gather all hard/soft IRQs usages backward in an
      * accumulated usage mask.
      */
     bfs_init_rootb(&this, prev);
 
     ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, usage_skip, NULL);
     if (bfs_error(ret)) {
         print_bfs_bug(ret);
         return 0;
     }
 
     usage_mask &= LOCKF_USED_IN_IRQ_ALL;
     if (!usage_mask)
         return 1;
 
     /*
      * Step 2: find exclusive uses forward that match the previous
      * backward accumulated mask.
      */
     forward_mask = exclusive_mask(usage_mask);
 
     bfs_init_root(&that, next);
 
     ret = find_usage_forwards(&that, forward_mask, &target_entry1);
     if (bfs_error(ret)) {
         print_bfs_bug(ret);
         return 0;
     }
     if (ret == BFS_RNOMATCH)
         return 1;
 
     /*
      * Step 3: we found a bad match! Now retrieve a lock from the backward
      * list whose usage mask matches the exclusive usage mask from the
      * lock found on the forward list.
      *
      * Note, we should only keep the LOCKF_ENABLED_IRQ_ALL bits, considering
      * the follow case:
      *
      * When trying to add A -> B to the graph, we find that there is a
      * hardirq-safe L, that L -> ... -> A, and another hardirq-unsafe M,
      * that B -> ... -> M. However M is **softirq-safe**, if we use exact
      * invert bits of M's usage_mask, we will find another lock N that is
      * **softirq-unsafe** and N -> ... -> A, however N -> .. -> M will not
      * cause a inversion deadlock.
      */
     backward_mask = original_mask(target_entry1->class->usage_mask & LOCKF_ENABLED_IRQ_ALL);
 
     ret = find_usage_backwards(&this, backward_mask, &target_entry);
     if (bfs_error(ret)) {
         print_bfs_bug(ret);
         return 0;
     }
     if (DEBUG_LOCKS_WARN_ON(ret == BFS_RNOMATCH))
         return 1;
 
     /*
      * Step 4: narrow down to a pair of incompatible usage bits
      * and report it.
      */
     ret = find_exclusive_match(target_entry->class->usage_mask,
                    target_entry1->class->usage_mask,
                    &backward_bit, &forward_bit);
     if (DEBUG_LOCKS_WARN_ON(ret == -1))
         return 1;
 
     print_bad_irq_dependency(curr, &this, &that,
                  target_entry, target_entry1,
                  prev, next,
                  backward_bit, forward_bit,
                  state_name(backward_bit));
 
     return 0;
 }
 
 #else
 
 static inline int check_irq_usage(struct task_struct *curr,
                   struct held_lock *prev, struct held_lock *next)
 {
     return 1;
 }
 
 static inline bool usage_skip(struct lock_list *entry, void *mask)
 {
     return false;
 }
 
 #endif /* CONFIG_TRACE_IRQFLAGS */
 
 #ifdef CONFIG_LOCKDEP_SMALL
 /*
  * Check that the dependency graph starting at <src> can lead to
  * <target> or not. If it can, <src> -> <target> dependency is already
  * in the graph.
  *
  * Return BFS_RMATCH if it does, or BFS_RNOMATCH if it does not, return BFS_E* if
  * any error appears in the bfs search.
  */
 static noinline enum bfs_result
 check_redundant(struct held_lock *src, struct held_lock *target)
 {
     enum bfs_result ret;
     struct lock_list *target_entry;
     struct lock_list src_entry;
 
     bfs_init_root(&src_entry, src);
     /*
      * Special setup for check_redundant().
      *
      * To report redundant, we need to find a strong dependency path that
      * is equal to or stronger than <src> -> <target>. So if <src> is E,
      * we need to let __bfs() only search for a path starting at a -(E*)->,
      * we achieve this by setting the initial node's ->only_xr to true in
      * that case. And if <prev> is S, we set initial ->only_xr to false
      * because both -(S*)-> (equal) and -(E*)-> (stronger) are redundant.
      */
     src_entry.only_xr = src->read == 0;
 
     debug_atomic_inc(nr_redundant_checks);
 
     /*
      * Note: we skip local_lock() for redundant check, because as the
      * comment in usage_skip(), A -> local_lock() -> B and A -> B are not
      * the same.
      */
     ret = check_path(target, &src_entry, hlock_equal, usage_skip, &target_entry);
 
     if (ret == BFS_RMATCH)
         debug_atomic_inc(nr_redundant);
 
     return ret;
 }
 
 #else
 
 static inline enum bfs_result
 check_redundant(struct held_lock *src, struct held_lock *target)
 {
     return BFS_RNOMATCH;
 }
 
 #endif
 
 static void inc_chains(int irq_context)
 {
     if (irq_context & LOCK_CHAIN_HARDIRQ_CONTEXT)
         nr_hardirq_chains++;
     else if (irq_context & LOCK_CHAIN_SOFTIRQ_CONTEXT)
         nr_softirq_chains++;
     else
         nr_process_chains++;
 }
 
 static void dec_chains(int irq_context)
 {
     if (irq_context & LOCK_CHAIN_HARDIRQ_CONTEXT)
         nr_hardirq_chains--;
     else if (irq_context & LOCK_CHAIN_SOFTIRQ_CONTEXT)
         nr_softirq_chains--;
     else
         nr_process_chains--;
 }
 
 static void
 print_deadlock_scenario(struct held_lock *nxt, struct held_lock *prv)
 {
     struct lock_class *next = hlock_class(nxt);
     struct lock_class *prev = hlock_class(prv);
 
     printk(" Possible unsafe locking scenario:\n\n");
     printk("       CPU0\n");
     printk("       ----\n");
     printk("  lock(");
     __print_lock_name(prev);
     printk(KERN_CONT ");\n");
     printk("  lock(");
     __print_lock_name(next);
     printk(KERN_CONT ");\n");
     printk("\n *** DEADLOCK ***\n\n");
     printk(" May be due to missing lock nesting notation\n\n");
 }
 
 static void
 print_deadlock_bug(struct task_struct *curr, struct held_lock *prev,
            struct held_lock *next)
 {
     if (!debug_locks_off_graph_unlock() || debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("============================================\n");
     pr_warn("WARNING: possible recursive locking detected\n");
     print_kernel_ident();
     pr_warn("--------------------------------------------\n");
     pr_warn("%s/%d is trying to acquire lock:\n",
         curr->comm, task_pid_nr(curr));
     print_lock(next);
     pr_warn("\nbut task is already holding lock:\n");
     print_lock(prev);
 
     pr_warn("\nother info that might help us debug this:\n");
     print_deadlock_scenario(next, prev);
     lockdep_print_held_locks(curr);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 
 /*
  * Check whether we are holding such a class already.
  *
  * (Note that this has to be done separately, because the graph cannot
  * detect such classes of deadlocks.)
  *
  * Returns: 0 on deadlock detected, 1 on OK, 2 if another lock with the same
  * lock class is held but nest_lock is also held, i.e. we rely on the
  * nest_lock to avoid the deadlock.
  */
 static int
 check_deadlock(struct task_struct *curr, struct held_lock *next)
 {
     struct held_lock *prev;
     struct held_lock *nest = NULL;
     int i;
 
     for (i = 0; i < curr->lockdep_depth; i++) {
         prev = curr->held_locks + i;
 
         if (prev->instance == next->nest_lock)
             nest = prev;
 
         if (hlock_class(prev) != hlock_class(next))
             continue;
 
         /*
          * Allow read-after-read recursion of the same
          * lock class (i.e. read_lock(lock)+read_lock(lock)):
          */
         if ((next->read == 2) && prev->read)
             continue;
 
         /*
          * We're holding the nest_lock, which serializes this lock's
          * nesting behaviour.
          */
         if (nest)
             return 2;
 
         print_deadlock_bug(curr, prev, next);
         return 0;
     }
     return 1;
 }
 
 /*
  * There was a chain-cache miss, and we are about to add a new dependency
  * to a previous lock. We validate the following rules:
  *
  *  - would the adding of the <prev> -> <next> dependency create a
  *    circular dependency in the graph? [== circular deadlock]
  *
  *  - does the new prev->next dependency connect any hardirq-safe lock
  *    (in the full backwards-subgraph starting at <prev>) with any
  *    hardirq-unsafe lock (in the full forwards-subgraph starting at
  *    <next>)? [== illegal lock inversion with hardirq contexts]
  *
  *  - does the new prev->next dependency connect any softirq-safe lock
  *    (in the full backwards-subgraph starting at <prev>) with any
  *    softirq-unsafe lock (in the full forwards-subgraph starting at
  *    <next>)? [== illegal lock inversion with softirq contexts]
  *
  * any of these scenarios could lead to a deadlock.
  *
  * Then if all the validations pass, we add the forwards and backwards
  * dependency.
  */
 static int
 check_prev_add(struct task_struct *curr, struct held_lock *prev,
            struct held_lock *next, u16 distance,
            struct lock_trace **const trace)
 {
     struct lock_list *entry;
     enum bfs_result ret;
 
     if (!hlock_class(prev)->key || !hlock_class(next)->key) {
         /*
          * The warning statements below may trigger a use-after-free
          * of the class name. It is better to trigger a use-after free
          * and to have the class name most of the time instead of not
          * having the class name available.
          */
         WARN_ONCE(!debug_locks_silent && !hlock_class(prev)->key,
               "Detected use-after-free of lock class %px/%s\n",
               hlock_class(prev),
               hlock_class(prev)->name);
         WARN_ONCE(!debug_locks_silent && !hlock_class(next)->key,
               "Detected use-after-free of lock class %px/%s\n",
               hlock_class(next),
               hlock_class(next)->name);
         return 2;
     }
 
     /*
      * Prove that the new <prev> -> <next> dependency would not
      * create a circular dependency in the graph. (We do this by
      * a breadth-first search into the graph starting at <next>,
      * and check whether we can reach <prev>.)
      *
      * The search is limited by the size of the circular queue (i.e.,
      * MAX_CIRCULAR_QUEUE_SIZE) which keeps track of a breadth of nodes
      * in the graph whose neighbours are to be checked.
      */
     ret = check_noncircular(next, prev, trace);
     if (unlikely(bfs_error(ret) || ret == BFS_RMATCH))
         return 0;
 
     if (!check_irq_usage(curr, prev, next))
         return 0;
 
     /*
      * Is the <prev> -> <next> dependency already present?
      *
      * (this may occur even though this is a new chain: consider
      *  e.g. the L1 -> L2 -> L3 -> L4 and the L5 -> L1 -> L2 -> L3
      *  chains - the second one will be new, but L1 already has
      *  L2 added to its dependency list, due to the first chain.)
      */
     list_for_each_entry(entry, &hlock_class(prev)->locks_after, entry) {
         if (entry->class == hlock_class(next)) {
             if (distance == 1)
                 entry->distance = 1;
             entry->dep |= calc_dep(prev, next);
 
             /*
              * Also, update the reverse dependency in @next's
              * ->locks_before list.
              *
              *  Here we reuse @entry as the cursor, which is fine
              *  because we won't go to the next iteration of the
              *  outer loop:
              *
              *  For normal cases, we return in the inner loop.
              *
              *  If we fail to return, we have inconsistency, i.e.
              *  <prev>::locks_after contains <next> while
              *  <next>::locks_before doesn't contain <prev>. In
              *  that case, we return after the inner and indicate
              *  something is wrong.
              */
             list_for_each_entry(entry, &hlock_class(next)->locks_before, entry) {
                 if (entry->class == hlock_class(prev)) {
                     if (distance == 1)
                         entry->distance = 1;
                     entry->dep |= calc_depb(prev, next);
                     return 1;
                 }
             }
 
             /* <prev> is not found in <next>::locks_before */
             return 0;
         }
     }
 
     /*
      * Is the <prev> -> <next> link redundant?
      */
     ret = check_redundant(prev, next);
     if (bfs_error(ret))
         return 0;
     else if (ret == BFS_RMATCH)
         return 2;
 
     if (!*trace) {
         *trace = save_trace();
         if (!*trace)
             return 0;
     }
 
     /*
      * Ok, all validations passed, add the new lock
      * to the previous lock's dependency list:
      */
     ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
                    &hlock_class(prev)->locks_after, distance,
                    calc_dep(prev, next), *trace);
 
     if (!ret)
         return 0;
 
     ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
                    &hlock_class(next)->locks_before, distance,
                    calc_depb(prev, next), *trace);
     if (!ret)
         return 0;
 
     return 2;
 }
 
 /*
  * Add the dependency to all directly-previous locks that are 'relevant'.
  * The ones that are relevant are (in increasing distance from curr):
  * all consecutive trylock entries and the final non-trylock entry - or
  * the end of this context's lock-chain - whichever comes first.
  */
 static int
 check_prevs_add(struct task_struct *curr, struct held_lock *next)
 {
     struct lock_trace *trace = NULL;
     int depth = curr->lockdep_depth;
     struct held_lock *hlock;
 
     /*
      * Debugging checks.
      *
      * Depth must not be zero for a non-head lock:
      */
     if (!depth)
         goto out_bug;
     /*
      * At least two relevant locks must exist for this
      * to be a head:
      */
     if (curr->held_locks[depth].irq_context !=
             curr->held_locks[depth-1].irq_context)
         goto out_bug;
 
     for (;;) {
         u16 distance = curr->lockdep_depth - depth + 1;
         hlock = curr->held_locks + depth - 1;
 
         if (hlock->check) {
             int ret = check_prev_add(curr, hlock, next, distance, &trace);
             if (!ret)
                 return 0;
 
             /*
              * Stop after the first non-trylock entry,
              * as non-trylock entries have added their
              * own direct dependencies already, so this
              * lock is connected to them indirectly:
              */
             if (!hlock->trylock)
                 break;
         }
 
         depth--;
         /*
          * End of lock-stack?
          */
         if (!depth)
             break;
         /*
          * Stop the search if we cross into another context:
          */
         if (curr->held_locks[depth].irq_context !=
                 curr->held_locks[depth-1].irq_context)
             break;
     }
     return 1;
 out_bug:
     if (!debug_locks_off_graph_unlock())
         return 0;
 
     /*
      * Clearly we all shouldn't be here, but since we made it we
      * can reliable say we messed up our state. See the above two
      * gotos for reasons why we could possibly end up here.
      */
     WARN_ON(1);
 
     return 0;
 }
 
 struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];
 static DECLARE_BITMAP(lock_chains_in_use, MAX_LOCKDEP_CHAINS);
 static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
 unsigned long nr_zapped_lock_chains;
 unsigned int nr_free_chain_hlocks;  /* Free chain_hlocks in buckets */
 unsigned int nr_lost_chain_hlocks;  /* Lost chain_hlocks */
 unsigned int nr_large_chain_blocks; /* size > MAX_CHAIN_BUCKETS */
 
 /*
  * The first 2 chain_hlocks entries in the chain block in the bucket
  * list contains the following meta data:
  *
  *   entry[0]:
  *     Bit    15 - always set to 1 (it is not a class index)
  *     Bits 0-14 - upper 15 bits of the next block index
  *   entry[1]    - lower 16 bits of next block index
  *
  * A next block index of all 1 bits means it is the end of the list.
  *
  * On the unsized bucket (bucket-0), the 3rd and 4th entries contain
  * the chain block size:
  *
  *   entry[2] - upper 16 bits of the chain block size
  *   entry[3] - lower 16 bits of the chain block size
  */
 #define MAX_CHAIN_BUCKETS   16
 #define CHAIN_BLK_FLAG      (1U << 15)
 #define CHAIN_BLK_LIST_END  0xFFFFU
 
 static int chain_block_buckets[MAX_CHAIN_BUCKETS];
 
 static inline int size_to_bucket(int size)
 {
     if (size > MAX_CHAIN_BUCKETS)
         return 0;
 
     return size - 1;
 }
 
 /*
  * Iterate all the chain blocks in a bucket.
  */
 #define for_each_chain_block(bucket, prev, curr)        \
     for ((prev) = -1, (curr) = chain_block_buckets[bucket]; \
          (curr) >= 0;                   \
          (prev) = (curr), (curr) = chain_block_next(curr))
 
 /*
  * next block or -1
  */
 static inline int chain_block_next(int offset)
 {
     int next = chain_hlocks[offset];
 
     WARN_ON_ONCE(!(next & CHAIN_BLK_FLAG));
 
     if (next == CHAIN_BLK_LIST_END)
         return -1;
 
     next &= ~CHAIN_BLK_FLAG;
     next <<= 16;
     next |= chain_hlocks[offset + 1];
 
     return next;
 }
 
 /*
  * bucket-0 only
  */
 static inline int chain_block_size(int offset)
 {
     return (chain_hlocks[offset + 2] << 16) | chain_hlocks[offset + 3];
 }
 
 static inline void init_chain_block(int offset, int next, int bucket, int size)
 {
     chain_hlocks[offset] = (next >> 16) | CHAIN_BLK_FLAG;
     chain_hlocks[offset + 1] = (u16)next;
 
     if (size && !bucket) {
         chain_hlocks[offset + 2] = size >> 16;
         chain_hlocks[offset + 3] = (u16)size;
     }
 }
 
 static inline void add_chain_block(int offset, int size)
 {
     int bucket = size_to_bucket(size);
     int next = chain_block_buckets[bucket];
     int prev, curr;
 
     if (unlikely(size < 2)) {
         /*
          * We can't store single entries on the freelist. Leak them.
          *
          * One possible way out would be to uniquely mark them, other
          * than with CHAIN_BLK_FLAG, such that we can recover them when
          * the block before it is re-added.
          */
         if (size)
             nr_lost_chain_hlocks++;
         return;
     }
 
     nr_free_chain_hlocks += size;
     if (!bucket) {
         nr_large_chain_blocks++;
 
         /*
          * Variable sized, sort large to small.
          */
         for_each_chain_block(0, prev, curr) {
             if (size >= chain_block_size(curr))
                 break;
         }
         init_chain_block(offset, curr, 0, size);
         if (prev < 0)
             chain_block_buckets[0] = offset;
         else
             init_chain_block(prev, offset, 0, 0);
         return;
     }
     /*
      * Fixed size, add to head.
      */
     init_chain_block(offset, next, bucket, size);
     chain_block_buckets[bucket] = offset;
 }
 
 /*
  * Only the first block in the list can be deleted.
  *
  * For the variable size bucket[0], the first block (the largest one) is
  * returned, broken up and put back into the pool. So if a chain block of
  * length > MAX_CHAIN_BUCKETS is ever used and zapped, it will just be
  * queued up after the primordial chain block and never be used until the
  * hlock entries in the primordial chain block is almost used up. That
  * causes fragmentation and reduce allocation efficiency. That can be
  * monitored by looking at the "large chain blocks" number in lockdep_stats.
  */
 static inline void del_chain_block(int bucket, int size, int next)
 {
     nr_free_chain_hlocks -= size;
     chain_block_buckets[bucket] = next;
 
     if (!bucket)
         nr_large_chain_blocks--;
 }
 
 static void init_chain_block_buckets(void)
 {
     int i;
 
     for (i = 0; i < MAX_CHAIN_BUCKETS; i++)
         chain_block_buckets[i] = -1;
 
     add_chain_block(0, ARRAY_SIZE(chain_hlocks));
 }
 
 /*
  * Return offset of a chain block of the right size or -1 if not found.
  *
  * Fairly simple worst-fit allocator with the addition of a number of size
  * specific free lists.
  */
 static int alloc_chain_hlocks(int req)
 {
     int bucket, curr, size;
 
     /*
      * We rely on the MSB to act as an escape bit to denote freelist
      * pointers. Make sure this bit isn't set in 'normal' class_idx usage.
      */
     BUILD_BUG_ON((MAX_LOCKDEP_KEYS-1) & CHAIN_BLK_FLAG);
 
     init_data_structures_once();
 
     if (nr_free_chain_hlocks < req)
         return -1;
 
     /*
      * We require a minimum of 2 (u16) entries to encode a freelist
      * 'pointer'.
      */
     req = max(req, 2);
     bucket = size_to_bucket(req);
     curr = chain_block_buckets[bucket];
 
     if (bucket) {
         if (curr >= 0) {
             del_chain_block(bucket, req, chain_block_next(curr));
             return curr;
         }
         /* Try bucket 0 */
         curr = chain_block_buckets[0];
     }
 
     /*
      * The variable sized freelist is sorted by size; the first entry is
      * the largest. Use it if it fits.
      */
     if (curr >= 0) {
         size = chain_block_size(curr);
         if (likely(size >= req)) {
             del_chain_block(0, size, chain_block_next(curr));
             add_chain_block(curr + req, size - req);
             return curr;
         }
     }
 
     /*
      * Last resort, split a block in a larger sized bucket.
      */
     for (size = MAX_CHAIN_BUCKETS; size > req; size--) {
         bucket = size_to_bucket(size);
         curr = chain_block_buckets[bucket];
         if (curr < 0)
             continue;
 
         del_chain_block(bucket, size, chain_block_next(curr));
         add_chain_block(curr + req, size - req);
         return curr;
     }
 
     return -1;
 }
 
 static inline void free_chain_hlocks(int base, int size)
 {
     add_chain_block(base, max(size, 2));
 }
 
 struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
 {
     u16 chain_hlock = chain_hlocks[chain->base + i];
     unsigned int class_idx = chain_hlock_class_idx(chain_hlock);
 
     return lock_classes + class_idx;
 }
 
 /*
  * Returns the index of the first held_lock of the current chain
  */
 static inline int get_first_held_lock(struct task_struct *curr,
                     struct held_lock *hlock)
 {
     int i;
     struct held_lock *hlock_curr;
 
     for (i = curr->lockdep_depth - 1; i >= 0; i--) {
         hlock_curr = curr->held_locks + i;
         if (hlock_curr->irq_context != hlock->irq_context)
             break;
 
     }
 
     return ++i;
 }
 
 #ifdef CONFIG_DEBUG_LOCKDEP
 /*
  * Returns the next chain_key iteration
  */
 static u64 print_chain_key_iteration(u16 hlock_id, u64 chain_key)
 {
     u64 new_chain_key = iterate_chain_key(chain_key, hlock_id);
 
     printk(" hlock_id:%d -> chain_key:%016Lx",
         (unsigned int)hlock_id,
         (unsigned long long)new_chain_key);
     return new_chain_key;
 }
 
 static void
 print_chain_keys_held_locks(struct task_struct *curr, struct held_lock *hlock_next)
 {
     struct held_lock *hlock;
     u64 chain_key = INITIAL_CHAIN_KEY;
     int depth = curr->lockdep_depth;
     int i = get_first_held_lock(curr, hlock_next);
 
     printk("depth: %u (irq_context %u)\n", depth - i + 1,
         hlock_next->irq_context);
     for (; i < depth; i++) {
         hlock = curr->held_locks + i;
         chain_key = print_chain_key_iteration(hlock_id(hlock), chain_key);
 
         print_lock(hlock);
     }
 
     print_chain_key_iteration(hlock_id(hlock_next), chain_key);
     print_lock(hlock_next);
 }
 
 static void print_chain_keys_chain(struct lock_chain *chain)
 {
     int i;
     u64 chain_key = INITIAL_CHAIN_KEY;
     u16 hlock_id;
 
     printk("depth: %u\n", chain->depth);
     for (i = 0; i < chain->depth; i++) {
         hlock_id = chain_hlocks[chain->base + i];
         chain_key = print_chain_key_iteration(hlock_id, chain_key);
 
         print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id));
         printk("\n");
     }
 }
 
 static void print_collision(struct task_struct *curr,
             struct held_lock *hlock_next,
             struct lock_chain *chain)
 {
     pr_warn("\n");
     pr_warn("============================\n");
     pr_warn("WARNING: chain_key collision\n");
     print_kernel_ident();
     pr_warn("----------------------------\n");
     pr_warn("%s/%d: ", current->comm, task_pid_nr(current));
     pr_warn("Hash chain already cached but the contents don't match!\n");
 
     pr_warn("Held locks:");
     print_chain_keys_held_locks(curr, hlock_next);
 
     pr_warn("Locks in cached chain:");
     print_chain_keys_chain(chain);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 #endif
 
 /*
  * Checks whether the chain and the current held locks are consistent
  * in depth and also in content. If they are not it most likely means
  * that there was a collision during the calculation of the chain_key.
  * Returns: 0 not passed, 1 passed
  */
 static int check_no_collision(struct task_struct *curr,
             struct held_lock *hlock,
             struct lock_chain *chain)
 {
 #ifdef CONFIG_DEBUG_LOCKDEP
     int i, j, id;
 
     i = get_first_held_lock(curr, hlock);
 
     if (DEBUG_LOCKS_WARN_ON(chain->depth != curr->lockdep_depth - (i - 1))) {
         print_collision(curr, hlock, chain);
         return 0;
     }
 
     for (j = 0; j < chain->depth - 1; j++, i++) {
         id = hlock_id(&curr->held_locks[i]);
 
         if (DEBUG_LOCKS_WARN_ON(chain_hlocks[chain->base + j] != id)) {
             print_collision(curr, hlock, chain);
             return 0;
         }
     }
 #endif
     return 1;
 }
 
 /*
  * Given an index that is >= -1, return the index of the next lock chain.
  * Return -2 if there is no next lock chain.
  */
 long lockdep_next_lockchain(long i)
 {
     i = find_next_bit(lock_chains_in_use, ARRAY_SIZE(lock_chains), i + 1);
     return i < ARRAY_SIZE(lock_chains) ? i : -2;
 }
 
 unsigned long lock_chain_count(void)
 {
     return bitmap_weight(lock_chains_in_use, ARRAY_SIZE(lock_chains));
 }
 
 /* Must be called with the graph lock held. */
 static struct lock_chain *alloc_lock_chain(void)
 {
     int idx = find_first_zero_bit(lock_chains_in_use,
                       ARRAY_SIZE(lock_chains));
 
     if (unlikely(idx >= ARRAY_SIZE(lock_chains)))
         return NULL;
     __set_bit(idx, lock_chains_in_use);
     return lock_chains + idx;
 }
 
 /*
  * Adds a dependency chain into chain hashtable. And must be called with
  * graph_lock held.
  *
  * Return 0 if fail, and graph_lock is released.
  * Return 1 if succeed, with graph_lock held.
  */
 static inline int add_chain_cache(struct task_struct *curr,
                   struct held_lock *hlock,
                   u64 chain_key)
 {
     struct hlist_head *hash_head = chainhashentry(chain_key);
     struct lock_chain *chain;
     int i, j;
 
     /*
      * The caller must hold the graph lock, ensure we've got IRQs
      * disabled to make this an IRQ-safe lock.. for recursion reasons
      * lockdep won't complain about its own locking errors.
      */
     if (lockdep_assert_locked())
         return 0;
 
     chain = alloc_lock_chain();
     if (!chain) {
         if (!debug_locks_off_graph_unlock())
             return 0;
 
         print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!");
         dump_stack();
         return 0;
     }
     chain->chain_key = chain_key;
     chain->irq_context = hlock->irq_context;
     i = get_first_held_lock(curr, hlock);
     chain->depth = curr->lockdep_depth + 1 - i;
 
     BUILD_BUG_ON((1UL << 24) <= ARRAY_SIZE(chain_hlocks));
     BUILD_BUG_ON((1UL << 6)  <= ARRAY_SIZE(curr->held_locks));
     BUILD_BUG_ON((1UL << 8*sizeof(chain_hlocks[0])) <= ARRAY_SIZE(lock_classes));
 
     j = alloc_chain_hlocks(chain->depth);
     if (j < 0) {
         if (!debug_locks_off_graph_unlock())
             return 0;
 
         print_lockdep_off("BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!");
         dump_stack();
         return 0;
     }
 
     chain->base = j;
     for (j = 0; j < chain->depth - 1; j++, i++) {
         int lock_id = hlock_id(curr->held_locks + i);
 
         chain_hlocks[chain->base + j] = lock_id;
     }
     chain_hlocks[chain->base + j] = hlock_id(hlock);
     hlist_add_head_rcu(&chain->entry, hash_head);
     debug_atomic_inc(chain_lookup_misses);
     inc_chains(chain->irq_context);
 
     return 1;
 }
 
 /*
  * Look up a dependency chain. Must be called with either the graph lock or
  * the RCU read lock held.
  */
 static inline struct lock_chain *lookup_chain_cache(u64 chain_key)
 {
     struct hlist_head *hash_head = chainhashentry(chain_key);
     struct lock_chain *chain;
 
     hlist_for_each_entry_rcu(chain, hash_head, entry) {
         if (READ_ONCE(chain->chain_key) == chain_key) {
             debug_atomic_inc(chain_lookup_hits);
             return chain;
         }
     }
     return NULL;
 }
 
 /*
  * If the key is not present yet in dependency chain cache then
  * add it and return 1 - in this case the new dependency chain is
  * validated. If the key is already hashed, return 0.
  * (On return with 1 graph_lock is held.)
  */
 static inline int lookup_chain_cache_add(struct task_struct *curr,
                      struct held_lock *hlock,
                      u64 chain_key)
 {
     struct lock_class *class = hlock_class(hlock);
     struct lock_chain *chain = lookup_chain_cache(chain_key);
 
     if (chain) {
 cache_hit:
         if (!check_no_collision(curr, hlock, chain))
             return 0;
 
         if (very_verbose(class)) {
             printk("\nhash chain already cached, key: "
                     "%016Lx tail class: [%px] %s\n",
                     (unsigned long long)chain_key,
                     class->key, class->name);
         }
 
         return 0;
     }
 
     if (very_verbose(class)) {
         printk("\nnew hash chain, key: %016Lx tail class: [%px] %s\n",
             (unsigned long long)chain_key, class->key, class->name);
     }
 
     if (!graph_lock())
         return 0;
 
     /*
      * We have to walk the chain again locked - to avoid duplicates:
      */
     chain = lookup_chain_cache(chain_key);
     if (chain) {
         graph_unlock();
         goto cache_hit;
     }
 
     if (!add_chain_cache(curr, hlock, chain_key))
         return 0;
 
     return 1;
 }
 
 static int validate_chain(struct task_struct *curr,
               struct held_lock *hlock,
               int chain_head, u64 chain_key)
 {
     /*
      * Trylock needs to maintain the stack of held locks, but it
      * does not add new dependencies, because trylock can be done
      * in any order.
      *
      * We look up the chain_key and do the O(N^2) check and update of
      * the dependencies only if this is a new dependency chain.
      * (If lookup_chain_cache_add() return with 1 it acquires
      * graph_lock for us)
      */
     if (!hlock->trylock && hlock->check &&
         lookup_chain_cache_add(curr, hlock, chain_key)) {
         /*
          * Check whether last held lock:
          *
          * - is irq-safe, if this lock is irq-unsafe
          * - is softirq-safe, if this lock is hardirq-unsafe
          *
          * And check whether the new lock's dependency graph
          * could lead back to the previous lock:
          *
          * - within the current held-lock stack
          * - across our accumulated lock dependency records
          *
          * any of these scenarios could lead to a deadlock.
          */
         /*
          * The simple case: does the current hold the same lock
          * already?
          */
         int ret = check_deadlock(curr, hlock);
 
         if (!ret)
             return 0;
         /*
          * Add dependency only if this lock is not the head
          * of the chain, and if the new lock introduces no more
          * lock dependency (because we already hold a lock with the
          * same lock class) nor deadlock (because the nest_lock
          * serializes nesting locks), see the comments for
          * check_deadlock().
          */
         if (!chain_head && ret != 2) {
             if (!check_prevs_add(curr, hlock))
                 return 0;
         }
 
         graph_unlock();
     } else {
         /* after lookup_chain_cache_add(): */
         if (unlikely(!debug_locks))
             return 0;
     }
 
     return 1;
 }
 #else
 static inline int validate_chain(struct task_struct *curr,
                  struct held_lock *hlock,
                  int chain_head, u64 chain_key)
 {
     return 1;
 }
 
 static void init_chain_block_buckets(void)  { }
 #endif /* CONFIG_PROVE_LOCKING */
 
 /*
  * We are building curr_chain_key incrementally, so double-check
  * it from scratch, to make sure that it's done correctly:
  */
 static void check_chain_key(struct task_struct *curr)
 {
 #ifdef CONFIG_DEBUG_LOCKDEP
     struct held_lock *hlock, *prev_hlock = NULL;
     unsigned int i;
     u64 chain_key = INITIAL_CHAIN_KEY;
 
     for (i = 0; i < curr->lockdep_depth; i++) {
         hlock = curr->held_locks + i;
         if (chain_key != hlock->prev_chain_key) {
             debug_locks_off();
             /*
              * We got mighty confused, our chain keys don't match
              * with what we expect, someone trample on our task state?
              */
             WARN(1, "hm#1, depth: %u [%u], %016Lx != %016Lx\n",
                 curr->lockdep_depth, i,
                 (unsigned long long)chain_key,
                 (unsigned long long)hlock->prev_chain_key);
             return;
         }
 
         /*
          * hlock->class_idx can't go beyond MAX_LOCKDEP_KEYS, but is
          * it registered lock class index?
          */
         if (DEBUG_LOCKS_WARN_ON(!test_bit(hlock->class_idx, lock_classes_in_use)))
             return;
 
         if (prev_hlock && (prev_hlock->irq_context !=
                             hlock->irq_context))
             chain_key = INITIAL_CHAIN_KEY;
         chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
         prev_hlock = hlock;
     }
     if (chain_key != curr->curr_chain_key) {
         debug_locks_off();
         /*
          * More smoking hash instead of calculating it, damn see these
          * numbers float.. I bet that a pink elephant stepped on my memory.
          */
         WARN(1, "hm#2, depth: %u [%u], %016Lx != %016Lx\n",
             curr->lockdep_depth, i,
             (unsigned long long)chain_key,
             (unsigned long long)curr->curr_chain_key);
     }
 #endif
 }
 
 #ifdef CONFIG_PROVE_LOCKING
 static int mark_lock(struct task_struct *curr, struct held_lock *this,
              enum lock_usage_bit new_bit);
 
 static void print_usage_bug_scenario(struct held_lock *lock)
 {
     struct lock_class *class = hlock_class(lock);
 
     printk(" Possible unsafe locking scenario:\n\n");
     printk("       CPU0\n");
     printk("       ----\n");
     printk("  lock(");
     __print_lock_name(class);
     printk(KERN_CONT ");\n");
     printk("  <Interrupt>\n");
     printk("    lock(");
     __print_lock_name(class);
     printk(KERN_CONT ");\n");
     printk("\n *** DEADLOCK ***\n\n");
 }
 
 static void
 print_usage_bug(struct task_struct *curr, struct held_lock *this,
         enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
 {
     if (!debug_locks_off() || debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("================================\n");
     pr_warn("WARNING: inconsistent lock state\n");
     print_kernel_ident();
     pr_warn("--------------------------------\n");
 
     pr_warn("inconsistent {%s} -> {%s} usage.\n",
         usage_str[prev_bit], usage_str[new_bit]);
 
     pr_warn("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] takes:\n",
         curr->comm, task_pid_nr(curr),
         lockdep_hardirq_context(), hardirq_count() >> HARDIRQ_SHIFT,
         lockdep_softirq_context(curr), softirq_count() >> SOFTIRQ_SHIFT,
         lockdep_hardirqs_enabled(),
         lockdep_softirqs_enabled(curr));
     print_lock(this);
 
     pr_warn("{%s} state was registered at:\n", usage_str[prev_bit]);
     print_lock_trace(hlock_class(this)->usage_traces[prev_bit], 1);
 
     print_irqtrace_events(curr);
     pr_warn("\nother info that might help us debug this:\n");
     print_usage_bug_scenario(this);
 
     lockdep_print_held_locks(curr);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 
 /*
  * Print out an error if an invalid bit is set:
  */
 static inline int
 valid_state(struct task_struct *curr, struct held_lock *this,
         enum lock_usage_bit new_bit, enum lock_usage_bit bad_bit)
 {
     if (unlikely(hlock_class(this)->usage_mask & (1 << bad_bit))) {
         graph_unlock();
         print_usage_bug(curr, this, bad_bit, new_bit);
         return 0;
     }
     return 1;
 }
 
 
 /*
  * print irq inversion bug:
  */
 static void
 print_irq_inversion_bug(struct task_struct *curr,
             struct lock_list *root, struct lock_list *other,
             struct held_lock *this, int forwards,
             const char *irqclass)
 {
     struct lock_list *entry = other;
     struct lock_list *middle = NULL;
     int depth;
 
     if (!debug_locks_off_graph_unlock() || debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("========================================================\n");
     pr_warn("WARNING: possible irq lock inversion dependency detected\n");
     print_kernel_ident();
     pr_warn("--------------------------------------------------------\n");
     pr_warn("%s/%d just changed the state of lock:\n",
         curr->comm, task_pid_nr(curr));
     print_lock(this);
     if (forwards)
         pr_warn("but this lock took another, %s-unsafe lock in the past:\n", irqclass);
     else
         pr_warn("but this lock was taken by another, %s-safe lock in the past:\n", irqclass);
     print_lock_name(other->class);
     pr_warn("\n\nand interrupts could create inverse lock ordering between them.\n\n");
 
     pr_warn("\nother info that might help us debug this:\n");
 
     /* Find a middle lock (if one exists) */
     depth = get_lock_depth(other);
     do {
         if (depth == 0 && (entry != root)) {
             pr_warn("lockdep:%s bad path found in chain graph\n", __func__);
             break;
         }
         middle = entry;
         entry = get_lock_parent(entry);
         depth--;
     } while (entry && entry != root && (depth >= 0));
     if (forwards)
         print_irq_lock_scenario(root, other,
             middle ? middle->class : root->class, other->class);
     else
         print_irq_lock_scenario(other, root,
             middle ? middle->class : other->class, root->class);
 
     lockdep_print_held_locks(curr);
 
     pr_warn("\nthe shortest dependencies between 2nd lock and 1st lock:\n");
     root->trace = save_trace();
     if (!root->trace)
         return;
     print_shortest_lock_dependencies(other, root);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 
 /*
  * Prove that in the forwards-direction subgraph starting at <this>
  * there is no lock matching <mask>:
  */
 static int
 check_usage_forwards(struct task_struct *curr, struct held_lock *this,
              enum lock_usage_bit bit)
 {
     enum bfs_result ret;
     struct lock_list root;
     struct lock_list *target_entry;
     enum lock_usage_bit read_bit = bit + LOCK_USAGE_READ_MASK;
     unsigned usage_mask = lock_flag(bit) | lock_flag(read_bit);
 
     bfs_init_root(&root, this);
     ret = find_usage_forwards(&root, usage_mask, &target_entry);
     if (bfs_error(ret)) {
         print_bfs_bug(ret);
         return 0;
     }
     if (ret == BFS_RNOMATCH)
         return 1;
 
     /* Check whether write or read usage is the match */
     if (target_entry->class->usage_mask & lock_flag(bit)) {
         print_irq_inversion_bug(curr, &root, target_entry,
                     this, 1, state_name(bit));
     } else {
         print_irq_inversion_bug(curr, &root, target_entry,
                     this, 1, state_name(read_bit));
     }
 
     return 0;
 }
 
 /*
  * Prove that in the backwards-direction subgraph starting at <this>
  * there is no lock matching <mask>:
  */
 static int
 check_usage_backwards(struct task_struct *curr, struct held_lock *this,
               enum lock_usage_bit bit)
 {
     enum bfs_result ret;
     struct lock_list root;
     struct lock_list *target_entry;
     enum lock_usage_bit read_bit = bit + LOCK_USAGE_READ_MASK;
     unsigned usage_mask = lock_flag(bit) | lock_flag(read_bit);
 
     bfs_init_rootb(&root, this);
     ret = find_usage_backwards(&root, usage_mask, &target_entry);
     if (bfs_error(ret)) {
         print_bfs_bug(ret);
         return 0;
     }
     if (ret == BFS_RNOMATCH)
         return 1;
 
     /* Check whether write or read usage is the match */
     if (target_entry->class->usage_mask & lock_flag(bit)) {
         print_irq_inversion_bug(curr, &root, target_entry,
                     this, 0, state_name(bit));
     } else {
         print_irq_inversion_bug(curr, &root, target_entry,
                     this, 0, state_name(read_bit));
     }
 
     return 0;
 }
 
 void print_irqtrace_events(struct task_struct *curr)
 {
     const struct irqtrace_events *trace = &curr->irqtrace;
 
     printk("irq event stamp: %u\n", trace->irq_events);
     printk("hardirqs last  enabled at (%u): [<%px>] %pS\n",
         trace->hardirq_enable_event, (void *)trace->hardirq_enable_ip,
         (void *)trace->hardirq_enable_ip);
     printk("hardirqs last disabled at (%u): [<%px>] %pS\n",
         trace->hardirq_disable_event, (void *)trace->hardirq_disable_ip,
         (void *)trace->hardirq_disable_ip);
     printk("softirqs last  enabled at (%u): [<%px>] %pS\n",
         trace->softirq_enable_event, (void *)trace->softirq_enable_ip,
         (void *)trace->softirq_enable_ip);
     printk("softirqs last disabled at (%u): [<%px>] %pS\n",
         trace->softirq_disable_event, (void *)trace->softirq_disable_ip,
         (void *)trace->softirq_disable_ip);
 }
 
 static int HARDIRQ_verbose(struct lock_class *class)
 {
 #if HARDIRQ_VERBOSE
     return class_filter(class);
 #endif
     return 0;
 }
 
 static int SOFTIRQ_verbose(struct lock_class *class)
 {
 #if SOFTIRQ_VERBOSE
     return class_filter(class);
 #endif
     return 0;
 }
 
 static int (*state_verbose_f[])(struct lock_class *class) = {
 #define LOCKDEP_STATE(__STATE) \
     __STATE##_verbose,
 #include "lockdep_states.h"
 #undef LOCKDEP_STATE
 };
 
 static inline int state_verbose(enum lock_usage_bit bit,
                 struct lock_class *class)
 {
     return state_verbose_f[bit >> LOCK_USAGE_DIR_MASK](class);
 }
 
 typedef int (*check_usage_f)(struct task_struct *, struct held_lock *,
                  enum lock_usage_bit bit, const char *name);
 
 static int
 mark_lock_irq(struct task_struct *curr, struct held_lock *this,
         enum lock_usage_bit new_bit)
 {
     int excl_bit = exclusive_bit(new_bit);
     int read = new_bit & LOCK_USAGE_READ_MASK;
     int dir = new_bit & LOCK_USAGE_DIR_MASK;
 
     /*
      * Validate that this particular lock does not have conflicting
      * usage states.
      */
     if (!valid_state(curr, this, new_bit, excl_bit))
         return 0;
 
     /*
      * Check for read in write conflicts
      */
     if (!read && !valid_state(curr, this, new_bit,
                   excl_bit + LOCK_USAGE_READ_MASK))
         return 0;
 
 
     /*
      * Validate that the lock dependencies don't have conflicting usage
      * states.
      */
     if (dir) {
         /*
          * mark ENABLED has to look backwards -- to ensure no dependee
          * has USED_IN state, which, again, would allow  recursion deadlocks.
          */
         if (!check_usage_backwards(curr, this, excl_bit))
             return 0;
     } else {
         /*
          * mark USED_IN has to look forwards -- to ensure no dependency
          * has ENABLED state, which would allow recursion deadlocks.
          */
         if (!check_usage_forwards(curr, this, excl_bit))
             return 0;
     }
 
     if (state_verbose(new_bit, hlock_class(this)))
         return 2;
 
     return 1;
 }
 
 /*
  * Mark all held locks with a usage bit:
  */
 static int
 mark_held_locks(struct task_struct *curr, enum lock_usage_bit base_bit)
 {
     struct held_lock *hlock;
     int i;
 
     for (i = 0; i < curr->lockdep_depth; i++) {
         enum lock_usage_bit hlock_bit = base_bit;
         hlock = curr->held_locks + i;
 
         if (hlock->read)
             hlock_bit += LOCK_USAGE_READ_MASK;
 
         BUG_ON(hlock_bit >= LOCK_USAGE_STATES);
 
         if (!hlock->check)
             continue;
 
         if (!mark_lock(curr, hlock, hlock_bit))
             return 0;
     }
 
     return 1;
 }
 
 /*
  * Hardirqs will be enabled:
  */
 static void __trace_hardirqs_on_caller(void)
 {
     struct task_struct *curr = current;
 
     /*
      * We are going to turn hardirqs on, so set the
      * usage bit for all held locks:
      */
     if (!mark_held_locks(curr, LOCK_ENABLED_HARDIRQ))
         return;
     /*
      * If we have softirqs enabled, then set the usage
      * bit for all held locks. (disabled hardirqs prevented
      * this bit from being set before)
      */
     if (curr->softirqs_enabled)
         mark_held_locks(curr, LOCK_ENABLED_SOFTIRQ);
 }
 
 /**
  * lockdep_hardirqs_on_prepare - Prepare for enabling interrupts
  *
  * Invoked before a possible transition to RCU idle from exit to user or
  * guest mode. This ensures that all RCU operations are done before RCU
  * stops watching. After the RCU transition lockdep_hardirqs_on() has to be
  * invoked to set the final state.
  */
 void lockdep_hardirqs_on_prepare(void)
 {
     if (unlikely(!debug_locks))
         return;
 
     /*
      * NMIs do not (and cannot) track lock dependencies, nothing to do.
      */
     if (unlikely(in_nmi()))
         return;
 
     if (unlikely(this_cpu_read(lockdep_recursion)))
         return;
 
     if (unlikely(lockdep_hardirqs_enabled())) {
         /*
          * Neither irq nor preemption are disabled here
          * so this is racy by nature but losing one hit
          * in a stat is not a big deal.
          */
         __debug_atomic_inc(redundant_hardirqs_on);
         return;
     }
 
     /*
      * We're enabling irqs and according to our state above irqs weren't
      * already enabled, yet we find the hardware thinks they are in fact
      * enabled.. someone messed up their IRQ state tracing.
      */
     if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
         return;
 
     /*
      * See the fine text that goes along with this variable definition.
      */
     if (DEBUG_LOCKS_WARN_ON(early_boot_irqs_disabled))
         return;
 
     /*
      * Can't allow enabling interrupts while in an interrupt handler,
      * that's general bad form and such. Recursion, limited stack etc..
      */
     if (DEBUG_LOCKS_WARN_ON(lockdep_hardirq_context()))
         return;
 
     current->hardirq_chain_key = current->curr_chain_key;
 
     lockdep_recursion_inc();
     __trace_hardirqs_on_caller();
     lockdep_recursion_finish();
 }
 EXPORT_SYMBOL_GPL(lockdep_hardirqs_on_prepare);
 
 void noinstr lockdep_hardirqs_on(unsigned long ip)
 {
     struct irqtrace_events *trace = &current->irqtrace;
 
     if (unlikely(!debug_locks))
         return;
 
     /*
      * NMIs can happen in the middle of local_irq_{en,dis}able() where the
      * tracking state and hardware state are out of sync.
      *
      * NMIs must save lockdep_hardirqs_enabled() to restore IRQ state from,
      * and not rely on hardware state like normal interrupts.
      */
     if (unlikely(in_nmi())) {
         if (!IS_ENABLED(CONFIG_TRACE_IRQFLAGS_NMI))
             return;
 
         /*
          * Skip:
          *  - recursion check, because NMI can hit lockdep;
          *  - hardware state check, because above;
          *  - chain_key check, see lockdep_hardirqs_on_prepare().
          */
         goto skip_checks;
     }
 
     if (unlikely(this_cpu_read(lockdep_recursion)))
         return;
 
     if (lockdep_hardirqs_enabled()) {
         /*
          * Neither irq nor preemption are disabled here
          * so this is racy by nature but losing one hit
          * in a stat is not a big deal.
          */
         __debug_atomic_inc(redundant_hardirqs_on);
         return;
     }
 
     /*
      * We're enabling irqs and according to our state above irqs weren't
      * already enabled, yet we find the hardware thinks they are in fact
      * enabled.. someone messed up their IRQ state tracing.
      */
     if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
         return;
 
     /*
      * Ensure the lock stack remained unchanged between
      * lockdep_hardirqs_on_prepare() and lockdep_hardirqs_on().
      */
     DEBUG_LOCKS_WARN_ON(current->hardirq_chain_key !=
                 current->curr_chain_key);
 
 skip_checks:
     /* we'll do an OFF -> ON transition: */
     __this_cpu_write(hardirqs_enabled, 1);
     trace->hardirq_enable_ip = ip;
     trace->hardirq_enable_event = ++trace->irq_events;
     debug_atomic_inc(hardirqs_on_events);
 }
 EXPORT_SYMBOL_GPL(lockdep_hardirqs_on);
 
 /*
  * Hardirqs were disabled:
  */
 void noinstr lockdep_hardirqs_off(unsigned long ip)
 {
     if (unlikely(!debug_locks))
         return;
 
     /*
      * Matching lockdep_hardirqs_on(), allow NMIs in the middle of lockdep;
      * they will restore the software state. This ensures the software
      * state is consistent inside NMIs as well.
      */
     if (in_nmi()) {
         if (!IS_ENABLED(CONFIG_TRACE_IRQFLAGS_NMI))
             return;
     } else if (__this_cpu_read(lockdep_recursion))
         return;
 
     /*
      * So we're supposed to get called after you mask local IRQs, but for
      * some reason the hardware doesn't quite think you did a proper job.
      */
     if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
         return;
 
     if (lockdep_hardirqs_enabled()) {
         struct irqtrace_events *trace = &current->irqtrace;
 
         /*
          * We have done an ON -> OFF transition:
          */
         __this_cpu_write(hardirqs_enabled, 0);
         trace->hardirq_disable_ip = ip;
         trace->hardirq_disable_event = ++trace->irq_events;
         debug_atomic_inc(hardirqs_off_events);
     } else {
         debug_atomic_inc(redundant_hardirqs_off);
     }
 }
 EXPORT_SYMBOL_GPL(lockdep_hardirqs_off);
 
 /*
  * Softirqs will be enabled:
  */
 void lockdep_softirqs_on(unsigned long ip)
 {
     struct irqtrace_events *trace = &current->irqtrace;
 
     if (unlikely(!lockdep_enabled()))
         return;
 
     /*
      * We fancy IRQs being disabled here, see softirq.c, avoids
      * funny state and nesting things.
      */
     if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
         return;
 
     if (current->softirqs_enabled) {
         debug_atomic_inc(redundant_softirqs_on);
         return;
     }
 
     lockdep_recursion_inc();
     /*
      * We'll do an OFF -> ON transition:
      */
     current->softirqs_enabled = 1;
     trace->softirq_enable_ip = ip;
     trace->softirq_enable_event = ++trace->irq_events;
     debug_atomic_inc(softirqs_on_events);
     /*
      * We are going to turn softirqs on, so set the
      * usage bit for all held locks, if hardirqs are
      * enabled too:
      */
     if (lockdep_hardirqs_enabled())
         mark_held_locks(current, LOCK_ENABLED_SOFTIRQ);
     lockdep_recursion_finish();
 }
 
 /*
  * Softirqs were disabled:
  */
 void lockdep_softirqs_off(unsigned long ip)
 {
     if (unlikely(!lockdep_enabled()))
         return;
 
     /*
      * We fancy IRQs being disabled here, see softirq.c
      */
     if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
         return;
 
     if (current->softirqs_enabled) {
         struct irqtrace_events *trace = &current->irqtrace;
 
         /*
          * We have done an ON -> OFF transition:
          */
         current->softirqs_enabled = 0;
         trace->softirq_disable_ip = ip;
         trace->softirq_disable_event = ++trace->irq_events;
         debug_atomic_inc(softirqs_off_events);
         /*
          * Whoops, we wanted softirqs off, so why aren't they?
          */
         DEBUG_LOCKS_WARN_ON(!softirq_count());
     } else
         debug_atomic_inc(redundant_softirqs_off);
 }
 
 static int
 mark_usage(struct task_struct *curr, struct held_lock *hlock, int check)
 {
     if (!check)
         goto lock_used;
 
     /*
      * If non-trylock use in a hardirq or softirq context, then
      * mark the lock as used in these contexts:
      */
     if (!hlock->trylock) {
         if (hlock->read) {
             if (lockdep_hardirq_context())
                 if (!mark_lock(curr, hlock,
                         LOCK_USED_IN_HARDIRQ_READ))
                     return 0;
             if (curr->softirq_context)
                 if (!mark_lock(curr, hlock,
                         LOCK_USED_IN_SOFTIRQ_READ))
                     return 0;
         } else {
             if (lockdep_hardirq_context())
                 if (!mark_lock(curr, hlock, LOCK_USED_IN_HARDIRQ))
                     return 0;
             if (curr->softirq_context)
                 if (!mark_lock(curr, hlock, LOCK_USED_IN_SOFTIRQ))
                     return 0;
         }
     }
     if (!hlock->hardirqs_off) {
         if (hlock->read) {
             if (!mark_lock(curr, hlock,
                     LOCK_ENABLED_HARDIRQ_READ))
                 return 0;
             if (curr->softirqs_enabled)
                 if (!mark_lock(curr, hlock,
                         LOCK_ENABLED_SOFTIRQ_READ))
                     return 0;
         } else {
             if (!mark_lock(curr, hlock,
                     LOCK_ENABLED_HARDIRQ))
                 return 0;
             if (curr->softirqs_enabled)
                 if (!mark_lock(curr, hlock,
                         LOCK_ENABLED_SOFTIRQ))
                     return 0;
         }
     }
 
 lock_used:
     /* mark it as used: */
     if (!mark_lock(curr, hlock, LOCK_USED))
         return 0;
 
     return 1;
 }
 
 static inline unsigned int task_irq_context(struct task_struct *task)
 {
     return LOCK_CHAIN_HARDIRQ_CONTEXT * !!lockdep_hardirq_context() +
            LOCK_CHAIN_SOFTIRQ_CONTEXT * !!task->softirq_context;
 }
 
 static int separate_irq_context(struct task_struct *curr,
         struct held_lock *hlock)
 {
     unsigned int depth = curr->lockdep_depth;
 
     /*
      * Keep track of points where we cross into an interrupt context:
      */
     if (depth) {
         struct held_lock *prev_hlock;
 
         prev_hlock = curr->held_locks + depth-1;
         /*
          * If we cross into another context, reset the
          * hash key (this also prevents the checking and the
          * adding of the dependency to 'prev'):
          */
         if (prev_hlock->irq_context != hlock->irq_context)
             return 1;
     }
     return 0;
 }
 
 /*
  * Mark a lock with a usage bit, and validate the state transition:
  */
 static int mark_lock(struct task_struct *curr, struct held_lock *this,
                  enum lock_usage_bit new_bit)
 {
     unsigned int new_mask, ret = 1;
 
     if (new_bit >= LOCK_USAGE_STATES) {
         DEBUG_LOCKS_WARN_ON(1);
         return 0;
     }
 
     if (new_bit == LOCK_USED && this->read)
         new_bit = LOCK_USED_READ;
 
     new_mask = 1 << new_bit;
 
     /*
      * If already set then do not dirty the cacheline,
      * nor do any checks:
      */
     if (likely(hlock_class(this)->usage_mask & new_mask))
         return 1;
 
     if (!graph_lock())
         return 0;
     /*
      * Make sure we didn't race:
      */
     if (unlikely(hlock_class(this)->usage_mask & new_mask))
         goto unlock;
 
     if (!hlock_class(this)->usage_mask)
         debug_atomic_dec(nr_unused_locks);
 
     hlock_class(this)->usage_mask |= new_mask;
 
     if (new_bit < LOCK_TRACE_STATES) {
         if (!(hlock_class(this)->usage_traces[new_bit] = save_trace()))
             return 0;
     }
 
     if (new_bit < LOCK_USED) {
         ret = mark_lock_irq(curr, this, new_bit);
         if (!ret)
             return 0;
     }
 
 unlock:
     graph_unlock();
 
     /*
      * We must printk outside of the graph_lock:
      */
     if (ret == 2) {
         printk("\nmarked lock as {%s}:\n", usage_str[new_bit]);
         print_lock(this);
         print_irqtrace_events(curr);
         dump_stack();
     }
 
     return ret;
 }
 
 static inline short task_wait_context(struct task_struct *curr)
 {
     /*
      * Set appropriate wait type for the context; for IRQs we have to take
      * into account force_irqthread as that is implied by PREEMPT_RT.
      */
     if (lockdep_hardirq_context()) {
         /*
          * Check if force_irqthreads will run us threaded.
          */
         if (curr->hardirq_threaded || curr->irq_config)
             return LD_WAIT_CONFIG;
 
         return LD_WAIT_SPIN;
     } else if (curr->softirq_context) {
         /*
          * Softirqs are always threaded.
          */
         return LD_WAIT_CONFIG;
     }
 
     return LD_WAIT_MAX;
 }
 
 static int
 print_lock_invalid_wait_context(struct task_struct *curr,
                 struct held_lock *hlock)
 {
     short curr_inner;
 
     if (!debug_locks_off())
         return 0;
     if (debug_locks_silent)
         return 0;
 
     pr_warn("\n");
     pr_warn("=============================\n");
     pr_warn("[ BUG: Invalid wait context ]\n");
     print_kernel_ident();
     pr_warn("-----------------------------\n");
 
     pr_warn("%s/%d is trying to lock:\n", curr->comm, task_pid_nr(curr));
     print_lock(hlock);
 
     pr_warn("other info that might help us debug this:\n");
 
     curr_inner = task_wait_context(curr);
     pr_warn("context-{%d:%d}\n", curr_inner, curr_inner);
 
     lockdep_print_held_locks(curr);
 
     pr_warn("stack backtrace:\n");
     dump_stack();
 
     return 0;
 }
 
 /*
  * Verify the wait_type context.
  *
  * This check validates we take locks in the right wait-type order; that is it
  * ensures that we do not take mutexes inside spinlocks and do not attempt to
  * acquire spinlocks inside raw_spinlocks and the sort.
  *
  * The entire thing is slightly more complex because of RCU, RCU is a lock that
  * can be taken from (pretty much) any context but also has constraints.
  * However when taken in a stricter environment the RCU lock does not loosen
  * the constraints.
  *
  * Therefore we must look for the strictest environment in the lock stack and
  * compare that to the lock we're trying to acquire.
  */
 static int check_wait_context(struct task_struct *curr, struct held_lock *next)
 {
     u8 next_inner = hlock_class(next)->wait_type_inner;
     u8 next_outer = hlock_class(next)->wait_type_outer;
     u8 curr_inner;
     int depth;
 
     if (!next_inner || next->trylock)
         return 0;
 
     if (!next_outer)
         next_outer = next_inner;
 
     /*
      * Find start of current irq_context..
      */
     for (depth = curr->lockdep_depth - 1; depth >= 0; depth--) {
         struct held_lock *prev = curr->held_locks + depth;
         if (prev->irq_context != next->irq_context)
             break;
     }
     depth++;
 
     curr_inner = task_wait_context(curr);
 
     for (; depth < curr->lockdep_depth; depth++) {
         struct held_lock *prev = curr->held_locks + depth;
         u8 prev_inner = hlock_class(prev)->wait_type_inner;
 
         if (prev_inner) {
             /*
              * We can have a bigger inner than a previous one
              * when outer is smaller than inner, as with RCU.
              *
              * Also due to trylocks.
              */
             curr_inner = min(curr_inner, prev_inner);
         }
     }
 
     if (next_outer > curr_inner)
         return print_lock_invalid_wait_context(curr, next);
 
     return 0;
 }
 
 #else /* CONFIG_PROVE_LOCKING */
 
 static inline int
 mark_usage(struct task_struct *curr, struct held_lock *hlock, int check)
 {
     return 1;
 }
 
 static inline unsigned int task_irq_context(struct task_struct *task)
 {
     return 0;
 }
 
 static inline int separate_irq_context(struct task_struct *curr,
         struct held_lock *hlock)
 {
     return 0;
 }
 
 static inline int check_wait_context(struct task_struct *curr,
                      struct held_lock *next)
 {
     return 0;
 }
 
 #endif /* CONFIG_PROVE_LOCKING */
 
 /*
  * Initialize a lock instance's lock-class mapping info:
  */
 void lockdep_init_map_type(struct lockdep_map *lock, const char *name,
                 struct lock_class_key *key, int subclass,
                 u8 inner, u8 outer, u8 lock_type)
 {
     int i;
 
     for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
         lock->class_cache[i] = NULL;
 
 #ifdef CONFIG_LOCK_STAT
     lock->cpu = raw_smp_processor_id();
 #endif
 
     /*
      * Can't be having no nameless bastards around this place!
      */
     if (DEBUG_LOCKS_WARN_ON(!name)) {
         lock->name = "NULL";
         return;
     }
 
     lock->name = name;
 
     lock->wait_type_outer = outer;
     lock->wait_type_inner = inner;
     lock->lock_type = lock_type;
 
     /*
      * No key, no joy, we need to hash something.
      */
     if (DEBUG_LOCKS_WARN_ON(!key))
         return;
     /*
      * Sanity check, the lock-class key must either have been allocated
      * statically or must have been registered as a dynamic key.
      */
     if (!static_obj(key) && !is_dynamic_key(key)) {
         if (debug_locks)
             printk(KERN_ERR "BUG: key %px has not been registered!\n", key);
         DEBUG_LOCKS_WARN_ON(1);
         return;
     }
     lock->key = key;
 
     if (unlikely(!debug_locks))
         return;
 
     if (subclass) {
         unsigned long flags;
 
         if (DEBUG_LOCKS_WARN_ON(!lockdep_enabled()))
             return;
 
         raw_local_irq_save(flags);
         lockdep_recursion_inc();
         register_lock_class(lock, subclass, 1);
         lockdep_recursion_finish();
         raw_local_irq_restore(flags);
     }
 }
 EXPORT_SYMBOL_GPL(lockdep_init_map_type);
 
 struct lock_class_key __lockdep_no_validate__;
 EXPORT_SYMBOL_GPL(__lockdep_no_validate__);
 
 static void
 print_lock_nested_lock_not_held(struct task_struct *curr,
                 struct held_lock *hlock)
 {
     if (!debug_locks_off())
         return;
     if (debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("==================================\n");
     pr_warn("WARNING: Nested lock was not taken\n");
     print_kernel_ident();
     pr_warn("----------------------------------\n");
 
     pr_warn("%s/%d is trying to lock:\n", curr->comm, task_pid_nr(curr));
     print_lock(hlock);
 
     pr_warn("\nbut this task is not holding:\n");
     pr_warn("%s\n", hlock->nest_lock->name);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 
     pr_warn("\nother info that might help us debug this:\n");
     lockdep_print_held_locks(curr);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 
 static int __lock_is_held(const struct lockdep_map *lock, int read);
 
 /*
  * This gets called for every mutex_lock*()/spin_lock*() operation.
  * We maintain the dependency maps and validate the locking attempt:
  *
  * The callers must make sure that IRQs are disabled before calling it,
  * otherwise we could get an interrupt which would want to take locks,
  * which would end up in lockdep again.
  */
 static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
               int trylock, int read, int check, int hardirqs_off,
               struct lockdep_map *nest_lock, unsigned long ip,
               int references, int pin_count)
 {
     struct task_struct *curr = current;
     struct lock_class *class = NULL;
     struct held_lock *hlock;
     unsigned int depth;
     int chain_head = 0;
     int class_idx;
     u64 chain_key;
 
     if (unlikely(!debug_locks))
         return 0;
 
     if (!prove_locking || lock->key == &__lockdep_no_validate__)
         check = 0;
 
     if (subclass < NR_LOCKDEP_CACHING_CLASSES)
         class = lock->class_cache[subclass];
     /*
      * Not cached?
      */
     if (unlikely(!class)) {
         class = register_lock_class(lock, subclass, 0);
         if (!class)
             return 0;
     }
 
     debug_class_ops_inc(class);
 
     if (very_verbose(class)) {
         printk("\nacquire class [%px] %s", class->key, class->name);
         if (class->name_version > 1)
             printk(KERN_CONT "#%d", class->name_version);
         printk(KERN_CONT "\n");
         dump_stack();
     }
 
     /*
      * Add the lock to the list of currently held locks.
      * (we dont increase the depth just yet, up until the
      * dependency checks are done)
      */
     depth = curr->lockdep_depth;
     /*
      * Ran out of static storage for our per-task lock stack again have we?
      */
     if (DEBUG_LOCKS_WARN_ON(depth >= MAX_LOCK_DEPTH))
         return 0;
 
     class_idx = class - lock_classes;
 
     if (depth) { /* we're holding locks */
         hlock = curr->held_locks + depth - 1;
         if (hlock->class_idx == class_idx && nest_lock) {
             if (!references)
                 references++;
 
             if (!hlock->references)
                 hlock->references++;
 
             hlock->references += references;
 
             /* Overflow */
             if (DEBUG_LOCKS_WARN_ON(hlock->references < references))
                 return 0;
 
             return 2;
         }
     }
 
     hlock = curr->held_locks + depth;
     /*
      * Plain impossible, we just registered it and checked it weren't no
      * NULL like.. I bet this mushroom I ate was good!
      */
     if (DEBUG_LOCKS_WARN_ON(!class))
         return 0;
     hlock->class_idx = class_idx;
     hlock->acquire_ip = ip;
     hlock->instance = lock;
     hlock->nest_lock = nest_lock;
     hlock->irq_context = task_irq_context(curr);
     hlock->trylock = trylock;
     hlock->read = read;
     hlock->check = check;
     hlock->hardirqs_off = !!hardirqs_off;
     hlock->references = references;
 #ifdef CONFIG_LOCK_STAT
     hlock->waittime_stamp = 0;
     hlock->holdtime_stamp = lockstat_clock();
 #endif
     hlock->pin_count = pin_count;
 
     if (check_wait_context(curr, hlock))
         return 0;
 
     /* Initialize the lock usage bit */
     if (!mark_usage(curr, hlock, check))
         return 0;
 
     /*
      * Calculate the chain hash: it's the combined hash of all the
      * lock keys along the dependency chain. We save the hash value
      * at every step so that we can get the current hash easily
      * after unlock. The chain hash is then used to cache dependency
      * results.
      *
      * The 'key ID' is what is the most compact key value to drive
      * the hash, not class->key.
      */
     /*
      * Whoops, we did it again.. class_idx is invalid.
      */
     if (DEBUG_LOCKS_WARN_ON(!test_bit(class_idx, lock_classes_in_use)))
         return 0;
 
     chain_key = curr->curr_chain_key;
     if (!depth) {
         /*
          * How can we have a chain hash when we ain't got no keys?!
          */
         if (DEBUG_LOCKS_WARN_ON(chain_key != INITIAL_CHAIN_KEY))
             return 0;
         chain_head = 1;
     }
 
     hlock->prev_chain_key = chain_key;
     if (separate_irq_context(curr, hlock)) {
         chain_key = INITIAL_CHAIN_KEY;
         chain_head = 1;
     }
     chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
 
     if (nest_lock && !__lock_is_held(nest_lock, -1)) {
         print_lock_nested_lock_not_held(curr, hlock);
         return 0;
     }
 
     if (!debug_locks_silent) {
         WARN_ON_ONCE(depth && !hlock_class(hlock - 1)->key);
         WARN_ON_ONCE(!hlock_class(hlock)->key);
     }
 
     if (!validate_chain(curr, hlock, chain_head, chain_key))
         return 0;
 
     curr->curr_chain_key = chain_key;
     curr->lockdep_depth++;
     check_chain_key(curr);
 #ifdef CONFIG_DEBUG_LOCKDEP
     if (unlikely(!debug_locks))
         return 0;
 #endif
     if (unlikely(curr->lockdep_depth >= MAX_LOCK_DEPTH)) {
         debug_locks_off();
         print_lockdep_off("BUG: MAX_LOCK_DEPTH too low!");
         printk(KERN_DEBUG "depth: %i  max: %lu!\n",
                curr->lockdep_depth, MAX_LOCK_DEPTH);
 
         lockdep_print_held_locks(current);
         debug_show_all_locks();
         dump_stack();
 
         return 0;
     }
 
     if (unlikely(curr->lockdep_depth > max_lockdep_depth))
         max_lockdep_depth = curr->lockdep_depth;
 
     return 1;
 }
 
 static void print_unlock_imbalance_bug(struct task_struct *curr,
                        struct lockdep_map *lock,
                        unsigned long ip)
 {
     if (!debug_locks_off())
         return;
     if (debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("=====================================\n");
     pr_warn("WARNING: bad unlock balance detected!\n");
     print_kernel_ident();
     pr_warn("-------------------------------------\n");
     pr_warn("%s/%d is trying to release lock (",
         curr->comm, task_pid_nr(curr));
     print_lockdep_cache(lock);
     pr_cont(") at:\n");
     print_ip_sym(KERN_WARNING, ip);
     pr_warn("but there are no more locks to release!\n");
     pr_warn("\nother info that might help us debug this:\n");
     lockdep_print_held_locks(curr);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 
 static noinstr int match_held_lock(const struct held_lock *hlock,
                    const struct lockdep_map *lock)
 {
     if (hlock->instance == lock)
         return 1;
 
     if (hlock->references) {
         const struct lock_class *class = lock->class_cache[0];
 
         if (!class)
             class = look_up_lock_class(lock, 0);
 
         /*
          * If look_up_lock_class() failed to find a class, we're trying
          * to test if we hold a lock that has never yet been acquired.
          * Clearly if the lock hasn't been acquired _ever_, we're not
          * holding it either, so report failure.
          */
         if (!class)
             return 0;
 
         /*
          * References, but not a lock we're actually ref-counting?
          * State got messed up, follow the sites that change ->references
          * and try to make sense of it.
          */
         if (DEBUG_LOCKS_WARN_ON(!hlock->nest_lock))
             return 0;
 
         if (hlock->class_idx == class - lock_classes)
             return 1;
     }
 
     return 0;
 }
 
 /* @depth must not be zero */
 static struct held_lock *find_held_lock(struct task_struct *curr,
                     struct lockdep_map *lock,
                     unsigned int depth, int *idx)
 {
     struct held_lock *ret, *hlock, *prev_hlock;
     int i;
 
     i = depth - 1;
     hlock = curr->held_locks + i;
     ret = hlock;
     if (match_held_lock(hlock, lock))
         goto out;
 
     ret = NULL;
     for (i--, prev_hlock = hlock--;
          i >= 0;
          i--, prev_hlock = hlock--) {
         /*
          * We must not cross into another context:
          */
         if (prev_hlock->irq_context != hlock->irq_context) {
             ret = NULL;
             break;
         }
         if (match_held_lock(hlock, lock)) {
             ret = hlock;
             break;
         }
     }
 
 out:
     *idx = i;
     return ret;
 }
 
 static int reacquire_held_locks(struct task_struct *curr, unsigned int depth,
                 int idx, unsigned int *merged)
 {
     struct held_lock *hlock;
     int first_idx = idx;
 
     if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
         return 0;
 
     for (hlock = curr->held_locks + idx; idx < depth; idx++, hlock++) {
         switch (__lock_acquire(hlock->instance,
                     hlock_class(hlock)->subclass,
                     hlock->trylock,
                     hlock->read, hlock->check,
                     hlock->hardirqs_off,
                     hlock->nest_lock, hlock->acquire_ip,
                     hlock->references, hlock->pin_count)) {
         case 0:
             return 1;
         case 1:
             break;
         case 2:
             *merged += (idx == first_idx);
             break;
         default:
             WARN_ON(1);
             return 0;
         }
     }
     return 0;
 }
 
 static int
 __lock_set_class(struct lockdep_map *lock, const char *name,
          struct lock_class_key *key, unsigned int subclass,
          unsigned long ip)
 {
     struct task_struct *curr = current;
     unsigned int depth, merged = 0;
     struct held_lock *hlock;
     struct lock_class *class;
     int i;
 
     if (unlikely(!debug_locks))
         return 0;
 
     depth = curr->lockdep_depth;
     /*
      * This function is about (re)setting the class of a held lock,
      * yet we're not actually holding any locks. Naughty user!
      */
     if (DEBUG_LOCKS_WARN_ON(!depth))
         return 0;
 
     hlock = find_held_lock(curr, lock, depth, &i);
     if (!hlock) {
         print_unlock_imbalance_bug(curr, lock, ip);
         return 0;
     }
 
     lockdep_init_map_type(lock, name, key, 0,
                   lock->wait_type_inner,
                   lock->wait_type_outer,
                   lock->lock_type);
     class = register_lock_class(lock, subclass, 0);
     hlock->class_idx = class - lock_classes;
 
     curr->lockdep_depth = i;
     curr->curr_chain_key = hlock->prev_chain_key;
 
     if (reacquire_held_locks(curr, depth, i, &merged))
         return 0;
 
     /*
      * I took it apart and put it back together again, except now I have
      * these 'spare' parts.. where shall I put them.
      */
     if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - merged))
         return 0;
     return 1;
 }
 
 static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
 {
     struct task_struct *curr = current;
     unsigned int depth, merged = 0;
     struct held_lock *hlock;
     int i;
 
     if (unlikely(!debug_locks))
         return 0;
 
     depth = curr->lockdep_depth;
     /*
      * This function is about (re)setting the class of a held lock,
      * yet we're not actually holding any locks. Naughty user!
      */
     if (DEBUG_LOCKS_WARN_ON(!depth))
         return 0;
 
     hlock = find_held_lock(curr, lock, depth, &i);
     if (!hlock) {
         print_unlock_imbalance_bug(curr, lock, ip);
         return 0;
     }
 
     curr->lockdep_depth = i;
     curr->curr_chain_key = hlock->prev_chain_key;
 
     WARN(hlock->read, "downgrading a read lock");
     hlock->read = 1;
     hlock->acquire_ip = ip;
 
     if (reacquire_held_locks(curr, depth, i, &merged))
         return 0;
 
     /* Merging can't happen with unchanged classes.. */
     if (DEBUG_LOCKS_WARN_ON(merged))
         return 0;
 
     /*
      * I took it apart and put it back together again, except now I have
      * these 'spare' parts.. where shall I put them.
      */
     if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
         return 0;
 
     return 1;
 }
 
 /*
  * Remove the lock from the list of currently held locks - this gets
  * called on mutex_unlock()/spin_unlock*() (or on a failed
  * mutex_lock_interruptible()).
  */
 static int
 __lock_release(struct lockdep_map *lock, unsigned long ip)
 {
     struct task_struct *curr = current;
     unsigned int depth, merged = 1;
     struct held_lock *hlock;
     int i;
 
     if (unlikely(!debug_locks))
         return 0;
 
     depth = curr->lockdep_depth;
     /*
      * So we're all set to release this lock.. wait what lock? We don't
      * own any locks, you've been drinking again?
      */
     if (depth <= 0) {
         print_unlock_imbalance_bug(curr, lock, ip);
         return 0;
     }
 
     /*
      * Check whether the lock exists in the current stack
      * of held locks:
      */
     hlock = find_held_lock(curr, lock, depth, &i);
     if (!hlock) {
         print_unlock_imbalance_bug(curr, lock, ip);
         return 0;
     }
 
     if (hlock->instance == lock)
         lock_release_holdtime(hlock);
 
     WARN(hlock->pin_count, "releasing a pinned lock\n");
 
     if (hlock->references) {
         hlock->references--;
         if (hlock->references) {
             /*
              * We had, and after removing one, still have
              * references, the current lock stack is still
              * valid. We're done!
              */
             return 1;
         }
     }
 
     /*
      * We have the right lock to unlock, 'hlock' points to it.
      * Now we remove it from the stack, and add back the other
      * entries (if any), recalculating the hash along the way:
      */
 
     curr->lockdep_depth = i;
     curr->curr_chain_key = hlock->prev_chain_key;
 
     /*
      * The most likely case is when the unlock is on the innermost
      * lock. In this case, we are done!
      */
     if (i == depth-1)
         return 1;
 
     if (reacquire_held_locks(curr, depth, i + 1, &merged))
         return 0;
 
     /*
      * We had N bottles of beer on the wall, we drank one, but now
      * there's not N-1 bottles of beer left on the wall...
      * Pouring two of the bottles together is acceptable.
      */
     DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - merged);
 
     /*
      * Since reacquire_held_locks() would have called check_chain_key()
      * indirectly via __lock_acquire(), we don't need to do it again
      * on return.
      */
     return 0;
 }
 
 static __always_inline
 int __lock_is_held(const struct lockdep_map *lock, int read)
 {
     struct task_struct *curr = current;
     int i;
 
     for (i = 0; i < curr->lockdep_depth; i++) {
         struct held_lock *hlock = curr->held_locks + i;
 
         if (match_held_lock(hlock, lock)) {
             if (read == -1 || !!hlock->read == read)
                 return LOCK_STATE_HELD;
 
             return LOCK_STATE_NOT_HELD;
         }
     }
 
     return LOCK_STATE_NOT_HELD;
 }
 
 static struct pin_cookie __lock_pin_lock(struct lockdep_map *lock)
 {
     struct pin_cookie cookie = NIL_COOKIE;
     struct task_struct *curr = current;
     int i;
 
     if (unlikely(!debug_locks))
         return cookie;
 
     for (i = 0; i < curr->lockdep_depth; i++) {
         struct held_lock *hlock = curr->held_locks + i;
 
         if (match_held_lock(hlock, lock)) {
             /*
              * Grab 16bits of randomness; this is sufficient to not
              * be guessable and still allows some pin nesting in
              * our u32 pin_count.
              */
             cookie.val = 1 + (sched_clock() & 0xffff);
             hlock->pin_count += cookie.val;
             return cookie;
         }
     }
 
     WARN(1, "pinning an unheld lock\n");
     return cookie;
 }
 
 static void __lock_repin_lock(struct lockdep_map *lock, struct pin_cookie cookie)
 {
     struct task_struct *curr = current;
     int i;
 
     if (unlikely(!debug_locks))
         return;
 
     for (i = 0; i < curr->lockdep_depth; i++) {
         struct held_lock *hlock = curr->held_locks + i;
 
         if (match_held_lock(hlock, lock)) {
             hlock->pin_count += cookie.val;
             return;
         }
     }
 
     WARN(1, "pinning an unheld lock\n");
 }
 
 static void __lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie cookie)
 {
     struct task_struct *curr = current;
     int i;
 
     if (unlikely(!debug_locks))
         return;
 
     for (i = 0; i < curr->lockdep_depth; i++) {
         struct held_lock *hlock = curr->held_locks + i;
 
         if (match_held_lock(hlock, lock)) {
             if (WARN(!hlock->pin_count, "unpinning an unpinned lock\n"))
                 return;
 
             hlock->pin_count -= cookie.val;
 
             if (WARN((int)hlock->pin_count < 0, "pin count corrupted\n"))
                 hlock->pin_count = 0;
 
             return;
         }
     }
 
     WARN(1, "unpinning an unheld lock\n");
 }
 
 /*
  * Check whether we follow the irq-flags state precisely:
  */
 static noinstr void check_flags(unsigned long flags)
 {
 #if defined(CONFIG_PROVE_LOCKING) && defined(CONFIG_DEBUG_LOCKDEP)
     if (!debug_locks)
         return;
 
     /* Get the warning out..  */
     instrumentation_begin();
 
     if (irqs_disabled_flags(flags)) {
         if (DEBUG_LOCKS_WARN_ON(lockdep_hardirqs_enabled())) {
             printk("possible reason: unannotated irqs-off.\n");
         }
     } else {
         if (DEBUG_LOCKS_WARN_ON(!lockdep_hardirqs_enabled())) {
             printk("possible reason: unannotated irqs-on.\n");
         }
     }
 
 #ifndef CONFIG_PREEMPT_RT
     /*
      * We dont accurately track softirq state in e.g.
      * hardirq contexts (such as on 4KSTACKS), so only
      * check if not in hardirq contexts:
      */
     if (!hardirq_count()) {
         if (softirq_count()) {
             /* like the above, but with softirqs */
             DEBUG_LOCKS_WARN_ON(current->softirqs_enabled);
         } else {
             /* lick the above, does it taste good? */
             DEBUG_LOCKS_WARN_ON(!current->softirqs_enabled);
         }
     }
 #endif
 
     if (!debug_locks)
         print_irqtrace_events(current);
 
     instrumentation_end();
 #endif
 }
 
 void lock_set_class(struct lockdep_map *lock, const char *name,
             struct lock_class_key *key, unsigned int subclass,
             unsigned long ip)
 {
     unsigned long flags;
 
     if (unlikely(!lockdep_enabled()))
         return;
 
     raw_local_irq_save(flags);
     lockdep_recursion_inc();
     check_flags(flags);
     if (__lock_set_class(lock, name, key, subclass, ip))
         check_chain_key(current);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lock_set_class);
 
 void lock_downgrade(struct lockdep_map *lock, unsigned long ip)
 {
     unsigned long flags;
 
     if (unlikely(!lockdep_enabled()))
         return;
 
     raw_local_irq_save(flags);
     lockdep_recursion_inc();
     check_flags(flags);
     if (__lock_downgrade(lock, ip))
         check_chain_key(current);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lock_downgrade);
 
 /* NMI context !!! */
 static void verify_lock_unused(struct lockdep_map *lock, struct held_lock *hlock, int subclass)
 {
 #ifdef CONFIG_PROVE_LOCKING
     struct lock_class *class = look_up_lock_class(lock, subclass);
     unsigned long mask = LOCKF_USED;
 
     /* if it doesn't have a class (yet), it certainly hasn't been used yet */
     if (!class)
         return;
 
     /*
      * READ locks only conflict with USED, such that if we only ever use
      * READ locks, there is no deadlock possible -- RCU.
      */
     if (!hlock->read)
         mask |= LOCKF_USED_READ;
 
     if (!(class->usage_mask & mask))
         return;
 
     hlock->class_idx = class - lock_classes;
 
     print_usage_bug(current, hlock, LOCK_USED, LOCK_USAGE_STATES);
 #endif
 }
 
 static bool lockdep_nmi(void)
 {
     if (raw_cpu_read(lockdep_recursion))
         return false;
 
     if (!in_nmi())
         return false;
 
     return true;
 }
 
 /*
  * read_lock() is recursive if:
  * 1. We force lockdep think this way in selftests or
  * 2. The implementation is not queued read/write lock or
  * 3. The locker is at an in_interrupt() context.
  */
 bool read_lock_is_recursive(void)
 {
     return force_read_lock_recursive ||
            !IS_ENABLED(CONFIG_QUEUED_RWLOCKS) ||
            in_interrupt();
 }
 EXPORT_SYMBOL_GPL(read_lock_is_recursive);
 
 /*
  * We are not always called with irqs disabled - do that here,
  * and also avoid lockdep recursion:
  */
 void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
               int trylock, int read, int check,
               struct lockdep_map *nest_lock, unsigned long ip)
 {
     unsigned long flags;
 
     trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
 
     if (!debug_locks)
         return;
 
     if (unlikely(!lockdep_enabled())) {
         /* XXX allow trylock from NMI ?!? */
         if (lockdep_nmi() && !trylock) {
             struct held_lock hlock;
 
             hlock.acquire_ip = ip;
             hlock.instance = lock;
             hlock.nest_lock = nest_lock;
             hlock.irq_context = 2; // XXX
             hlock.trylock = trylock;
             hlock.read = read;
             hlock.check = check;
             hlock.hardirqs_off = true;
             hlock.references = 0;
 
             verify_lock_unused(lock, &hlock, subclass);
         }
         return;
     }
 
     raw_local_irq_save(flags);
     check_flags(flags);
 
     lockdep_recursion_inc();
     __lock_acquire(lock, subclass, trylock, read, check,
                irqs_disabled_flags(flags), nest_lock, ip, 0, 0);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lock_acquire);
 
 void lock_release(struct lockdep_map *lock, unsigned long ip)
 {
     unsigned long flags;
 
     trace_lock_release(lock, ip);
 
     if (unlikely(!lockdep_enabled()))
         return;
 
     raw_local_irq_save(flags);
     check_flags(flags);
 
     lockdep_recursion_inc();
     if (__lock_release(lock, ip))
         check_chain_key(current);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lock_release);
 
 noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
 {
     unsigned long flags;
     int ret = LOCK_STATE_NOT_HELD;
 
     /*
      * Avoid false negative lockdep_assert_held() and
      * lockdep_assert_not_held().
      */
     if (unlikely(!lockdep_enabled()))
         return LOCK_STATE_UNKNOWN;
 
     raw_local_irq_save(flags);
     check_flags(flags);
 
     lockdep_recursion_inc();
     ret = __lock_is_held(lock, read);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(lock_is_held_type);
 NOKPROBE_SYMBOL(lock_is_held_type);
 
 struct pin_cookie lock_pin_lock(struct lockdep_map *lock)
 {
     struct pin_cookie cookie = NIL_COOKIE;
     unsigned long flags;
 
     if (unlikely(!lockdep_enabled()))
         return cookie;
 
     raw_local_irq_save(flags);
     check_flags(flags);
 
     lockdep_recursion_inc();
     cookie = __lock_pin_lock(lock);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 
     return cookie;
 }
 EXPORT_SYMBOL_GPL(lock_pin_lock);
 
 void lock_repin_lock(struct lockdep_map *lock, struct pin_cookie cookie)
 {
     unsigned long flags;
 
     if (unlikely(!lockdep_enabled()))
         return;
 
     raw_local_irq_save(flags);
     check_flags(flags);
 
     lockdep_recursion_inc();
     __lock_repin_lock(lock, cookie);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lock_repin_lock);
 
 void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie cookie)
 {
     unsigned long flags;
 
     if (unlikely(!lockdep_enabled()))
         return;
 
     raw_local_irq_save(flags);
     check_flags(flags);
 
     lockdep_recursion_inc();
     __lock_unpin_lock(lock, cookie);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lock_unpin_lock);
 
 #ifdef CONFIG_LOCK_STAT
 static void print_lock_contention_bug(struct task_struct *curr,
                       struct lockdep_map *lock,
                       unsigned long ip)
 {
     if (!debug_locks_off())
         return;
     if (debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("=================================\n");
     pr_warn("WARNING: bad contention detected!\n");
     print_kernel_ident();
     pr_warn("---------------------------------\n");
     pr_warn("%s/%d is trying to contend lock (",
         curr->comm, task_pid_nr(curr));
     print_lockdep_cache(lock);
     pr_cont(") at:\n");
     print_ip_sym(KERN_WARNING, ip);
     pr_warn("but there are no locks held!\n");
     pr_warn("\nother info that might help us debug this:\n");
     lockdep_print_held_locks(curr);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 
 static void
 __lock_contended(struct lockdep_map *lock, unsigned long ip)
 {
     struct task_struct *curr = current;
     struct held_lock *hlock;
     struct lock_class_stats *stats;
     unsigned int depth;
     int i, contention_point, contending_point;
 
     depth = curr->lockdep_depth;
     /*
      * Whee, we contended on this lock, except it seems we're not
      * actually trying to acquire anything much at all..
      */
     if (DEBUG_LOCKS_WARN_ON(!depth))
         return;
 
     hlock = find_held_lock(curr, lock, depth, &i);
     if (!hlock) {
         print_lock_contention_bug(curr, lock, ip);
         return;
     }
 
     if (hlock->instance != lock)
         return;
 
     hlock->waittime_stamp = lockstat_clock();
 
     contention_point = lock_point(hlock_class(hlock)->contention_point, ip);
     contending_point = lock_point(hlock_class(hlock)->contending_point,
                       lock->ip);
 
     stats = get_lock_stats(hlock_class(hlock));
     if (contention_point < LOCKSTAT_POINTS)
         stats->contention_point[contention_point]++;
     if (contending_point < LOCKSTAT_POINTS)
         stats->contending_point[contending_point]++;
     if (lock->cpu != smp_processor_id())
         stats->bounces[bounce_contended + !!hlock->read]++;
 }
 
 static void
 __lock_acquired(struct lockdep_map *lock, unsigned long ip)
 {
     struct task_struct *curr = current;
     struct held_lock *hlock;
     struct lock_class_stats *stats;
     unsigned int depth;
     u64 now, waittime = 0;
     int i, cpu;
 
     depth = curr->lockdep_depth;
     /*
      * Yay, we acquired ownership of this lock we didn't try to
      * acquire, how the heck did that happen?
      */
     if (DEBUG_LOCKS_WARN_ON(!depth))
         return;
 
     hlock = find_held_lock(curr, lock, depth, &i);
     if (!hlock) {
         print_lock_contention_bug(curr, lock, _RET_IP_);
         return;
     }
 
     if (hlock->instance != lock)
         return;
 
     cpu = smp_processor_id();
     if (hlock->waittime_stamp) {
         now = lockstat_clock();
         waittime = now - hlock->waittime_stamp;
         hlock->holdtime_stamp = now;
     }
 
     stats = get_lock_stats(hlock_class(hlock));
     if (waittime) {
         if (hlock->read)
             lock_time_inc(&stats->read_waittime, waittime);
         else
             lock_time_inc(&stats->write_waittime, waittime);
     }
     if (lock->cpu != cpu)
         stats->bounces[bounce_acquired + !!hlock->read]++;
 
     lock->cpu = cpu;
     lock->ip = ip;
 }
 
 void lock_contended(struct lockdep_map *lock, unsigned long ip)
 {
     unsigned long flags;
 
     trace_lock_contended(lock, ip);
 
     if (unlikely(!lock_stat || !lockdep_enabled()))
         return;
 
     raw_local_irq_save(flags);
     check_flags(flags);
     lockdep_recursion_inc();
     __lock_contended(lock, ip);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lock_contended);
 
 void lock_acquired(struct lockdep_map *lock, unsigned long ip)
 {
     unsigned long flags;
 
     trace_lock_acquired(lock, ip);
 
     if (unlikely(!lock_stat || !lockdep_enabled()))
         return;
 
     raw_local_irq_save(flags);
     check_flags(flags);
     lockdep_recursion_inc();
     __lock_acquired(lock, ip);
     lockdep_recursion_finish();
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lock_acquired);
 #endif
 
 /*
  * Used by the testsuite, sanitize the validator state
  * after a simulated failure:
  */
 
 void lockdep_reset(void)
 {
     unsigned long flags;
     int i;
 
     raw_local_irq_save(flags);
     lockdep_init_task(current);
     memset(current->held_locks, 0, MAX_LOCK_DEPTH*sizeof(struct held_lock));
     nr_hardirq_chains = 0;
     nr_softirq_chains = 0;
     nr_process_chains = 0;
     debug_locks = 1;
     for (i = 0; i < CHAINHASH_SIZE; i++)
         INIT_HLIST_HEAD(chainhash_table + i);
     raw_local_irq_restore(flags);
 }
 
 /* Remove a class from a lock chain. Must be called with the graph lock held. */
 static void remove_class_from_lock_chain(struct pending_free *pf,
                      struct lock_chain *chain,
                      struct lock_class *class)
 {
 #ifdef CONFIG_PROVE_LOCKING
     int i;
 
     for (i = chain->base; i < chain->base + chain->depth; i++) {
         if (chain_hlock_class_idx(chain_hlocks[i]) != class - lock_classes)
             continue;
         /*
          * Each lock class occurs at most once in a lock chain so once
          * we found a match we can break out of this loop.
          */
         goto free_lock_chain;
     }
     /* Since the chain has not been modified, return. */
     return;
 
 free_lock_chain:
     free_chain_hlocks(chain->base, chain->depth);
     /* Overwrite the chain key for concurrent RCU readers. */
     WRITE_ONCE(chain->chain_key, INITIAL_CHAIN_KEY);
     dec_chains(chain->irq_context);
 
     /*
      * Note: calling hlist_del_rcu() from inside a
      * hlist_for_each_entry_rcu() loop is safe.
      */
     hlist_del_rcu(&chain->entry);
     __set_bit(chain - lock_chains, pf->lock_chains_being_freed);
     nr_zapped_lock_chains++;
 #endif
 }
 
 /* Must be called with the graph lock held. */
 static void remove_class_from_lock_chains(struct pending_free *pf,
                       struct lock_class *class)
 {
     struct lock_chain *chain;
     struct hlist_head *head;
     int i;
 
     for (i = 0; i < ARRAY_SIZE(chainhash_table); i++) {
         head = chainhash_table + i;
         hlist_for_each_entry_rcu(chain, head, entry) {
             remove_class_from_lock_chain(pf, chain, class);
         }
     }
 }
 
 /*
  * Remove all references to a lock class. The caller must hold the graph lock.
  */
 static void zap_class(struct pending_free *pf, struct lock_class *class)
 {
     struct lock_list *entry;
     int i;
 
     WARN_ON_ONCE(!class->key);
 
     /*
      * Remove all dependencies this lock is
      * involved in:
      */
     for_each_set_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) {
         entry = list_entries + i;
         if (entry->class != class && entry->links_to != class)
             continue;
         __clear_bit(i, list_entries_in_use);
         nr_list_entries--;
         list_del_rcu(&entry->entry);
     }
     if (list_empty(&class->locks_after) &&
         list_empty(&class->locks_before)) {
         list_move_tail(&class->lock_entry, &pf->zapped);
         hlist_del_rcu(&class->hash_entry);
         WRITE_ONCE(class->key, NULL);
         WRITE_ONCE(class->name, NULL);
         nr_lock_classes--;
         __clear_bit(class - lock_classes, lock_classes_in_use);
         if (class - lock_classes == max_lock_class_idx)
             max_lock_class_idx--;
     } else {
         WARN_ONCE(true, "%s() failed for class %s\n", __func__,
               class->name);
     }
 
     remove_class_from_lock_chains(pf, class);
     nr_zapped_classes++;
 }
 
 static void reinit_class(struct lock_class *class)
 {
     WARN_ON_ONCE(!class->lock_entry.next);
     WARN_ON_ONCE(!list_empty(&class->locks_after));
     WARN_ON_ONCE(!list_empty(&class->locks_before));
     memset_startat(class, 0, key);
     WARN_ON_ONCE(!class->lock_entry.next);
     WARN_ON_ONCE(!list_empty(&class->locks_after));
     WARN_ON_ONCE(!list_empty(&class->locks_before));
 }
 
 static inline int within(const void *addr, void *start, unsigned long size)
 {
     return addr >= start && addr < start + size;
 }
 
 static bool inside_selftest(void)
 {
     return current == lockdep_selftest_task_struct;
 }
 
 /* The caller must hold the graph lock. */
 static struct pending_free *get_pending_free(void)
 {
     return delayed_free.pf + delayed_free.index;
 }
 
 static void free_zapped_rcu(struct rcu_head *cb);
 
 /*
  * Schedule an RCU callback if no RCU callback is pending. Must be called with
  * the graph lock held.
  */
 static void call_rcu_zapped(struct pending_free *pf)
 {
     WARN_ON_ONCE(inside_selftest());
 
     if (list_empty(&pf->zapped))
         return;
 
     if (delayed_free.scheduled)
         return;
 
     delayed_free.scheduled = true;
 
     WARN_ON_ONCE(delayed_free.pf + delayed_free.index != pf);
     delayed_free.index ^= 1;
 
     call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
 }
 
 /* The caller must hold the graph lock. May be called from RCU context. */
 static void __free_zapped_classes(struct pending_free *pf)
 {
     struct lock_class *class;
 
     check_data_structures();
 
     list_for_each_entry(class, &pf->zapped, lock_entry)
         reinit_class(class);
 
     list_splice_init(&pf->zapped, &free_lock_classes);
 
 #ifdef CONFIG_PROVE_LOCKING
     bitmap_andnot(lock_chains_in_use, lock_chains_in_use,
               pf->lock_chains_being_freed, ARRAY_SIZE(lock_chains));
     bitmap_clear(pf->lock_chains_being_freed, 0, ARRAY_SIZE(lock_chains));
 #endif
 }
 
 static void free_zapped_rcu(struct rcu_head *ch)
 {
     struct pending_free *pf;
     unsigned long flags;
 
     if (WARN_ON_ONCE(ch != &delayed_free.rcu_head))
         return;
 
     raw_local_irq_save(flags);
     lockdep_lock();
 
     /* closed head */
     pf = delayed_free.pf + (delayed_free.index ^ 1);
     __free_zapped_classes(pf);
     delayed_free.scheduled = false;
 
     /*
      * If there's anything on the open list, close and start a new callback.
      */
     call_rcu_zapped(delayed_free.pf + delayed_free.index);
 
     lockdep_unlock();
     raw_local_irq_restore(flags);
 }
 
 /*
  * Remove all lock classes from the class hash table and from the
  * all_lock_classes list whose key or name is in the address range [start,
  * start + size). Move these lock classes to the zapped_classes list. Must
  * be called with the graph lock held.
  */
 static void __lockdep_free_key_range(struct pending_free *pf, void *start,
                      unsigned long size)
 {
     struct lock_class *class;
     struct hlist_head *head;
     int i;
 
     /* Unhash all classes that were created by a module. */
     for (i = 0; i < CLASSHASH_SIZE; i++) {
         head = classhash_table + i;
         hlist_for_each_entry_rcu(class, head, hash_entry) {
             if (!within(class->key, start, size) &&
                 !within(class->name, start, size))
                 continue;
             zap_class(pf, class);
         }
     }
 }
 
 /*
  * Used in module.c to remove lock classes from memory that is going to be
  * freed; and possibly re-used by other modules.
  *
  * We will have had one synchronize_rcu() before getting here, so we're
  * guaranteed nobody will look up these exact classes -- they're properly dead
  * but still allocated.
  */
 static void lockdep_free_key_range_reg(void *start, unsigned long size)
 {
     struct pending_free *pf;
     unsigned long flags;
 
     init_data_structures_once();
 
     raw_local_irq_save(flags);
     lockdep_lock();
     pf = get_pending_free();
     __lockdep_free_key_range(pf, start, size);
     call_rcu_zapped(pf);
     lockdep_unlock();
     raw_local_irq_restore(flags);
 
     /*
      * Wait for any possible iterators from look_up_lock_class() to pass
      * before continuing to free the memory they refer to.
      */
     synchronize_rcu();
 }
 
 /*
  * Free all lockdep keys in the range [start, start+size). Does not sleep.
  * Ignores debug_locks. Must only be used by the lockdep selftests.
  */
 static void lockdep_free_key_range_imm(void *start, unsigned long size)
 {
     struct pending_free *pf = delayed_free.pf;
     unsigned long flags;
 
     init_data_structures_once();
 
     raw_local_irq_save(flags);
     lockdep_lock();
     __lockdep_free_key_range(pf, start, size);
     __free_zapped_classes(pf);
     lockdep_unlock();
     raw_local_irq_restore(flags);
 }
 
 void lockdep_free_key_range(void *start, unsigned long size)
 {
     init_data_structures_once();
 
     if (inside_selftest())
         lockdep_free_key_range_imm(start, size);
     else
         lockdep_free_key_range_reg(start, size);
 }
 
 /*
  * Check whether any element of the @lock->class_cache[] array refers to a
  * registered lock class. The caller must hold either the graph lock or the
  * RCU read lock.
  */
 static bool lock_class_cache_is_registered(struct lockdep_map *lock)
 {
     struct lock_class *class;
     struct hlist_head *head;
     int i, j;
 
     for (i = 0; i < CLASSHASH_SIZE; i++) {
         head = classhash_table + i;
         hlist_for_each_entry_rcu(class, head, hash_entry) {
             for (j = 0; j < NR_LOCKDEP_CACHING_CLASSES; j++)
                 if (lock->class_cache[j] == class)
                     return true;
         }
     }
     return false;
 }
 
 /* The caller must hold the graph lock. Does not sleep. */
 static void __lockdep_reset_lock(struct pending_free *pf,
                  struct lockdep_map *lock)
 {
     struct lock_class *class;
     int j;
 
     /*
      * Remove all classes this lock might have:
      */
     for (j = 0; j < MAX_LOCKDEP_SUBCLASSES; j++) {
         /*
          * If the class exists we look it up and zap it:
          */
         class = look_up_lock_class(lock, j);
         if (class)
             zap_class(pf, class);
     }
     /*
      * Debug check: in the end all mapped classes should
      * be gone.
      */
     if (WARN_ON_ONCE(lock_class_cache_is_registered(lock)))
         debug_locks_off();
 }
 
 /*
  * Remove all information lockdep has about a lock if debug_locks == 1. Free
  * released data structures from RCU context.
  */
 static void lockdep_reset_lock_reg(struct lockdep_map *lock)
 {
     struct pending_free *pf;
     unsigned long flags;
     int locked;
 
     raw_local_irq_save(flags);
     locked = graph_lock();
     if (!locked)
         goto out_irq;
 
     pf = get_pending_free();
     __lockdep_reset_lock(pf, lock);
     call_rcu_zapped(pf);
 
     graph_unlock();
 out_irq:
     raw_local_irq_restore(flags);
 }
 
 /*
  * Reset a lock. Does not sleep. Ignores debug_locks. Must only be used by the
  * lockdep selftests.
  */
 static void lockdep_reset_lock_imm(struct lockdep_map *lock)
 {
     struct pending_free *pf = delayed_free.pf;
     unsigned long flags;
 
     raw_local_irq_save(flags);
     lockdep_lock();
     __lockdep_reset_lock(pf, lock);
     __free_zapped_classes(pf);
     lockdep_unlock();
     raw_local_irq_restore(flags);
 }
 
 void lockdep_reset_lock(struct lockdep_map *lock)
 {
     init_data_structures_once();
 
     if (inside_selftest())
         lockdep_reset_lock_imm(lock);
     else
         lockdep_reset_lock_reg(lock);
 }
 
 /*
  * Unregister a dynamically allocated key.
  *
  * Unlike lockdep_register_key(), a search is always done to find a matching
  * key irrespective of debug_locks to avoid potential invalid access to freed
  * memory in lock_class entry.
  */
 void lockdep_unregister_key(struct lock_class_key *key)
 {
     struct hlist_head *hash_head = keyhashentry(key);
     struct lock_class_key *k;
     struct pending_free *pf;
     unsigned long flags;
     bool found = false;
 
     might_sleep();
 
     if (WARN_ON_ONCE(static_obj(key)))
         return;
 
     raw_local_irq_save(flags);
     lockdep_lock();
 
     hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
         if (k == key) {
             hlist_del_rcu(&k->hash_entry);
             found = true;
             break;
         }
     }
     WARN_ON_ONCE(!found && debug_locks);
     if (found) {
         pf = get_pending_free();
         __lockdep_free_key_range(pf, key, 1);
         call_rcu_zapped(pf);
     }
     lockdep_unlock();
     raw_local_irq_restore(flags);
 
     /* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
     synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(lockdep_unregister_key);
 
 void __init lockdep_init(void)
 {
     printk("Lock dependency validator: Copyright (c) 2006 Red Hat, Inc., Ingo Molnar\n");
 
     printk("... MAX_LOCKDEP_SUBCLASSES:  %lu\n", MAX_LOCKDEP_SUBCLASSES);
     printk("... MAX_LOCK_DEPTH:          %lu\n", MAX_LOCK_DEPTH);
     printk("... MAX_LOCKDEP_KEYS:        %lu\n", MAX_LOCKDEP_KEYS);
     printk("... CLASSHASH_SIZE:          %lu\n", CLASSHASH_SIZE);
     printk("... MAX_LOCKDEP_ENTRIES:     %lu\n", MAX_LOCKDEP_ENTRIES);
     printk("... MAX_LOCKDEP_CHAINS:      %lu\n", MAX_LOCKDEP_CHAINS);
     printk("... CHAINHASH_SIZE:          %lu\n", CHAINHASH_SIZE);
 
     printk(" memory used by lock dependency info: %zu kB\n",
            (sizeof(lock_classes) +
         sizeof(lock_classes_in_use) +
         sizeof(classhash_table) +
         sizeof(list_entries) +
         sizeof(list_entries_in_use) +
         sizeof(chainhash_table) +
         sizeof(delayed_free)
 #ifdef CONFIG_PROVE_LOCKING
         + sizeof(lock_cq)
         + sizeof(lock_chains)
         + sizeof(lock_chains_in_use)
         + sizeof(chain_hlocks)
 #endif
         ) / 1024
         );
 
 #if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
     printk(" memory used for stack traces: %zu kB\n",
            (sizeof(stack_trace) + sizeof(stack_trace_hash)) / 1024
            );
 #endif
 
     printk(" per task-struct memory footprint: %zu bytes\n",
            sizeof(((struct task_struct *)NULL)->held_locks));
 }
 
 static void
 print_freed_lock_bug(struct task_struct *curr, const void *mem_from,
              const void *mem_to, struct held_lock *hlock)
 {
     if (!debug_locks_off())
         return;
     if (debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("=========================\n");
     pr_warn("WARNING: held lock freed!\n");
     print_kernel_ident();
     pr_warn("-------------------------\n");
     pr_warn("%s/%d is freeing memory %px-%px, with a lock still held there!\n",
         curr->comm, task_pid_nr(curr), mem_from, mem_to-1);
     print_lock(hlock);
     lockdep_print_held_locks(curr);
 
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 
 static inline int not_in_range(const void* mem_from, unsigned long mem_len,
                 const void* lock_from, unsigned long lock_len)
 {
     return lock_from + lock_len <= mem_from ||
         mem_from + mem_len <= lock_from;
 }
 
 /*
  * Called when kernel memory is freed (or unmapped), or if a lock
  * is destroyed or reinitialized - this code checks whether there is
  * any held lock in the memory range of <from> to <to>:
  */
 void debug_check_no_locks_freed(const void *mem_from, unsigned long mem_len)
 {
     struct task_struct *curr = current;
     struct held_lock *hlock;
     unsigned long flags;
     int i;
 
     if (unlikely(!debug_locks))
         return;
 
     raw_local_irq_save(flags);
     for (i = 0; i < curr->lockdep_depth; i++) {
         hlock = curr->held_locks + i;
 
         if (not_in_range(mem_from, mem_len, hlock->instance,
                     sizeof(*hlock->instance)))
             continue;
 
         print_freed_lock_bug(curr, mem_from, mem_from + mem_len, hlock);
         break;
     }
     raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(debug_check_no_locks_freed);
 
 static void print_held_locks_bug(void)
 {
     if (!debug_locks_off())
         return;
     if (debug_locks_silent)
         return;
 
     pr_warn("\n");
     pr_warn("====================================\n");
     pr_warn("WARNING: %s/%d still has locks held!\n",
            current->comm, task_pid_nr(current));
     print_kernel_ident();
     pr_warn("------------------------------------\n");
     lockdep_print_held_locks(current);
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 
 void debug_check_no_locks_held(void)
 {
     if (unlikely(current->lockdep_depth > 0))
         print_held_locks_bug();
 }
 EXPORT_SYMBOL_GPL(debug_check_no_locks_held);
 
 #ifdef __KERNEL__
 void debug_show_all_locks(void)
 {
     struct task_struct *g, *p;
 
     if (unlikely(!debug_locks)) {
         pr_warn("INFO: lockdep is turned off.\n");
         return;
     }
     pr_warn("\nShowing all locks held in the system:\n");
 
     rcu_read_lock();
     for_each_process_thread(g, p) {
         if (!p->lockdep_depth)
             continue;
         lockdep_print_held_locks(p);
         touch_nmi_watchdog();
         touch_all_softlockup_watchdogs();
     }
     rcu_read_unlock();
 
     pr_warn("\n");
     pr_warn("=============================================\n\n");
 }
 EXPORT_SYMBOL_GPL(debug_show_all_locks);
 #endif
 
 /*
  * Careful: only use this function if you are sure that
  * the task cannot run in parallel!
  */
 void debug_show_held_locks(struct task_struct *task)
 {
     if (unlikely(!debug_locks)) {
         printk("INFO: lockdep is turned off.\n");
         return;
     }
     lockdep_print_held_locks(task);
 }
 EXPORT_SYMBOL_GPL(debug_show_held_locks);
 
 asmlinkage __visible void lockdep_sys_exit(void)
 {
     struct task_struct *curr = current;
 
     if (unlikely(curr->lockdep_depth)) {
         if (!debug_locks_off())
             return;
         pr_warn("\n");
         pr_warn("================================================\n");
         pr_warn("WARNING: lock held when returning to user space!\n");
         print_kernel_ident();
         pr_warn("------------------------------------------------\n");
         pr_warn("%s/%d is leaving the kernel with locks still held!\n",
                 curr->comm, curr->pid);
         lockdep_print_held_locks(curr);
     }
 
     /*
      * The lock history for each syscall should be independent. So wipe the
      * slate clean on return to userspace.
      */
     lockdep_invariant_state(false);
 }
 
 void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
 {
     struct task_struct *curr = current;
     int dl = READ_ONCE(debug_locks);
 
     /* Note: the following can be executed concurrently, so be careful. */
     pr_warn("\n");
     pr_warn("=============================\n");
     pr_warn("WARNING: suspicious RCU usage\n");
     print_kernel_ident();
     pr_warn("-----------------------------\n");
     pr_warn("%s:%d %s!\n", file, line, s);
     pr_warn("\nother info that might help us debug this:\n\n");
     pr_warn("\n%srcu_scheduler_active = %d, debug_locks = %d\n%s",
            !rcu_lockdep_current_cpu_online()
             ? "RCU used illegally from offline CPU!\n"
             : "",
            rcu_scheduler_active, dl,
            dl ? "" : "Possible false positive due to lockdep disabling via debug_locks = 0\n");
 
     /*
      * If a CPU is in the RCU-free window in idle (ie: in the section
      * between ct_idle_enter() and ct_idle_exit(), then RCU
      * considers that CPU to be in an "extended quiescent state",
      * which means that RCU will be completely ignoring that CPU.
      * Therefore, rcu_read_lock() and friends have absolutely no
      * effect on a CPU running in that state. In other words, even if
      * such an RCU-idle CPU has called rcu_read_lock(), RCU might well
      * delete data structures out from under it.  RCU really has no
      * choice here: we need to keep an RCU-free window in idle where
      * the CPU may possibly enter into low power mode. This way we can
      * notice an extended quiescent state to other CPUs that started a grace
      * period. Otherwise we would delay any grace period as long as we run
      * in the idle task.
      *
      * So complain bitterly if someone does call rcu_read_lock(),
      * rcu_read_lock_bh() and so on from extended quiescent states.
      */
     if (!rcu_is_watching())
         pr_warn("RCU used illegally from extended quiescent state!\n");
 
     lockdep_print_held_locks(curr);
     pr_warn("\nstack backtrace:\n");
     dump_stack();
 }
 EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);