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 /* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Read-Copy Update mechanism for mutual exclusion
  *
  * Copyright IBM Corporation, 2001
  *
  * Author: Dipankar Sarma <dipankar@in.ibm.com>
  *
  * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com>
  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  * Papers:
  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
  *
  * For detailed explanation of Read-Copy Update mechanism see -
  *      http://lse.sourceforge.net/locking/rcupdate.html
  *
  */
 
 #ifndef __LINUX_RCUPDATE_H
 #define __LINUX_RCUPDATE_H
 
 #include <linux/types.h>
 #include <linux/compiler.h>
 #include <linux/atomic.h>
 #include <linux/irqflags.h>
 #include <linux/preempt.h>
 #include <linux/bottom_half.h>
 #include <linux/lockdep.h>
 #include <asm/processor.h>
 #include <linux/cpumask.h>
 #include <linux/context_tracking_irq.h>
 
 #define ULONG_CMP_GE(a, b)  (ULONG_MAX / 2 >= (a) - (b))
 #define ULONG_CMP_LT(a, b)  (ULONG_MAX / 2 < (a) - (b))
 #define ulong2long(a)       (*(long *)(&(a)))
 #define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
 #define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b)))
 
 /* Exported common interfaces */
 void call_rcu(struct rcu_head *head, rcu_callback_t func);
 void rcu_barrier_tasks(void);
 void rcu_barrier_tasks_rude(void);
 void synchronize_rcu(void);
 unsigned long get_completed_synchronize_rcu(void);
 
 #ifdef CONFIG_PREEMPT_RCU
 
 void __rcu_read_lock(void);
 void __rcu_read_unlock(void);
 
 /*
  * Defined as a macro as it is a very low level header included from
  * areas that don't even know about current.  This gives the rcu_read_lock()
  * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
  */
 #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
 
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
 #ifdef CONFIG_TINY_RCU
 #define rcu_read_unlock_strict() do { } while (0)
 #else
 void rcu_read_unlock_strict(void);
 #endif
 
 static inline void __rcu_read_lock(void)
 {
     preempt_disable();
 }
 
 static inline void __rcu_read_unlock(void)
 {
     preempt_enable();
     if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
         rcu_read_unlock_strict();
 }
 
 static inline int rcu_preempt_depth(void)
 {
     return 0;
 }
 
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
 /* Internal to kernel */
 void rcu_init(void);
 extern int rcu_scheduler_active;
 void rcu_sched_clock_irq(int user);
 void rcu_report_dead(unsigned int cpu);
 void rcutree_migrate_callbacks(int cpu);
 
 #ifdef CONFIG_TASKS_RCU_GENERIC
 void rcu_init_tasks_generic(void);
 #else
 static inline void rcu_init_tasks_generic(void) { }
 #endif
 
 #ifdef CONFIG_RCU_STALL_COMMON
 void rcu_sysrq_start(void);
 void rcu_sysrq_end(void);
 #else /* #ifdef CONFIG_RCU_STALL_COMMON */
 static inline void rcu_sysrq_start(void) { }
 static inline void rcu_sysrq_end(void) { }
 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
 
 #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
 void rcu_irq_work_resched(void);
 #else
 static inline void rcu_irq_work_resched(void) { }
 #endif
 
 #ifdef CONFIG_RCU_NOCB_CPU
 void rcu_init_nohz(void);
 int rcu_nocb_cpu_offload(int cpu);
 int rcu_nocb_cpu_deoffload(int cpu);
 void rcu_nocb_flush_deferred_wakeup(void);
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 static inline void rcu_init_nohz(void) { }
 static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
 static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
 static inline void rcu_nocb_flush_deferred_wakeup(void) { }
 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
 
 /**
  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
  * @a: Code that RCU needs to pay attention to.
  *
  * RCU read-side critical sections are forbidden in the inner idle loop,
  * that is, between the ct_idle_enter() and the ct_idle_exit() -- RCU
  * will happily ignore any such read-side critical sections.  However,
  * things like powertop need tracepoints in the inner idle loop.
  *
  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
  * will tell RCU that it needs to pay attention, invoke its argument
  * (in this example, calling the do_something_with_RCU() function),
  * and then tell RCU to go back to ignoring this CPU.  It is permissible
  * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
  * on the order of a million or so, even on 32-bit systems).  It is
  * not legal to block within RCU_NONIDLE(), nor is it permissible to
  * transfer control either into or out of RCU_NONIDLE()'s statement.
  */
 #define RCU_NONIDLE(a) \
     do { \
         ct_irq_enter_irqson(); \
         do { a; } while (0); \
         ct_irq_exit_irqson(); \
     } while (0)
 
 /*
  * Note a quasi-voluntary context switch for RCU-tasks's benefit.
  * This is a macro rather than an inline function to avoid #include hell.
  */
 #ifdef CONFIG_TASKS_RCU_GENERIC
 
 # ifdef CONFIG_TASKS_RCU
 # define rcu_tasks_classic_qs(t, preempt)               \
     do {                                \
         if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout))    \
             WRITE_ONCE((t)->rcu_tasks_holdout, false);  \
     } while (0)
 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
 void synchronize_rcu_tasks(void);
 # else
 # define rcu_tasks_classic_qs(t, preempt) do { } while (0)
 # define call_rcu_tasks call_rcu
 # define synchronize_rcu_tasks synchronize_rcu
 # endif
 
 # ifdef CONFIG_TASKS_TRACE_RCU
 // Bits for ->trc_reader_special.b.need_qs field.
 #define TRC_NEED_QS     0x1  // Task needs a quiescent state.
 #define TRC_NEED_QS_CHECKED 0x2  // Task has been checked for needing quiescent state.
 
 u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new);
 void rcu_tasks_trace_qs_blkd(struct task_struct *t);
 
 # define rcu_tasks_trace_qs(t)                          \
     do {                                    \
         int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting);   \
                                         \
         if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) &&    \
             likely(!___rttq_nesting)) {                 \
             rcu_trc_cmpxchg_need_qs((t), 0, TRC_NEED_QS_CHECKED);   \
         } else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \
                !READ_ONCE((t)->trc_reader_special.b.blocked)) { \
             rcu_tasks_trace_qs_blkd(t);             \
         }                               \
     } while (0)
 # else
 # define rcu_tasks_trace_qs(t) do { } while (0)
 # endif
 
 #define rcu_tasks_qs(t, preempt)                    \
 do {                                    \
     rcu_tasks_classic_qs((t), (preempt));               \
     rcu_tasks_trace_qs(t);                      \
 } while (0)
 
 # ifdef CONFIG_TASKS_RUDE_RCU
 void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func);
 void synchronize_rcu_tasks_rude(void);
 # endif
 
 #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
 void exit_tasks_rcu_start(void);
 void exit_tasks_rcu_finish(void);
 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
 #define rcu_tasks_classic_qs(t, preempt) do { } while (0)
 #define rcu_tasks_qs(t, preempt) do { } while (0)
 #define rcu_note_voluntary_context_switch(t) do { } while (0)
 #define call_rcu_tasks call_rcu
 #define synchronize_rcu_tasks synchronize_rcu
 static inline void exit_tasks_rcu_start(void) { }
 static inline void exit_tasks_rcu_finish(void) { }
 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
 
 /**
  * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
  *
  * This macro resembles cond_resched(), except that it is defined to
  * report potential quiescent states to RCU-tasks even if the cond_resched()
  * machinery were to be shut off, as some advocate for PREEMPTION kernels.
  */
 #define cond_resched_tasks_rcu_qs() \
 do { \
     rcu_tasks_qs(current, false); \
     cond_resched(); \
 } while (0)
 
 /*
  * Infrastructure to implement the synchronize_() primitives in
  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
  */
 
 #if defined(CONFIG_TREE_RCU)
 #include <linux/rcutree.h>
 #elif defined(CONFIG_TINY_RCU)
 #include <linux/rcutiny.h>
 #else
 #error "Unknown RCU implementation specified to kernel configuration"
 #endif
 
 /*
  * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
  * are needed for dynamic initialization and destruction of rcu_head
  * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
  * dynamic initialization and destruction of statically allocated rcu_head
  * structures.  However, rcu_head structures allocated dynamically in the
  * heap don't need any initialization.
  */
 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 void init_rcu_head(struct rcu_head *head);
 void destroy_rcu_head(struct rcu_head *head);
 void init_rcu_head_on_stack(struct rcu_head *head);
 void destroy_rcu_head_on_stack(struct rcu_head *head);
 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 static inline void init_rcu_head(struct rcu_head *head) { }
 static inline void destroy_rcu_head(struct rcu_head *head) { }
 static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
 static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 
 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
 bool rcu_lockdep_current_cpu_online(void);
 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
 static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
 
 extern struct lockdep_map rcu_lock_map;
 extern struct lockdep_map rcu_bh_lock_map;
 extern struct lockdep_map rcu_sched_lock_map;
 extern struct lockdep_map rcu_callback_map;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 static inline void rcu_lock_acquire(struct lockdep_map *map)
 {
     lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
 }
 
 static inline void rcu_lock_release(struct lockdep_map *map)
 {
     lock_release(map, _THIS_IP_);
 }
 
 int debug_lockdep_rcu_enabled(void);
 int rcu_read_lock_held(void);
 int rcu_read_lock_bh_held(void);
 int rcu_read_lock_sched_held(void);
 int rcu_read_lock_any_held(void);
 
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 # define rcu_lock_acquire(a)        do { } while (0)
 # define rcu_lock_release(a)        do { } while (0)
 
 static inline int rcu_read_lock_held(void)
 {
     return 1;
 }
 
 static inline int rcu_read_lock_bh_held(void)
 {
     return 1;
 }
 
 static inline int rcu_read_lock_sched_held(void)
 {
     return !preemptible();
 }
 
 static inline int rcu_read_lock_any_held(void)
 {
     return !preemptible();
 }
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 #ifdef CONFIG_PROVE_RCU
 
 /**
  * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
  * @c: condition to check
  * @s: informative message
  */
 #define RCU_LOCKDEP_WARN(c, s)                      \
     do {                                \
         static bool __section(".data.unlikely") __warned;   \
         if ((c) && debug_lockdep_rcu_enabled() && !__warned) {  \
             __warned = true;                \
             lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
         }                           \
     } while (0)
 
 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
 static inline void rcu_preempt_sleep_check(void)
 {
     RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
              "Illegal context switch in RCU read-side critical section");
 }
 #else /* #ifdef CONFIG_PROVE_RCU */
 static inline void rcu_preempt_sleep_check(void) { }
 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 
 #define rcu_sleep_check()                       \
     do {                                \
         rcu_preempt_sleep_check();              \
         if (!IS_ENABLED(CONFIG_PREEMPT_RT))         \
             RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),    \
                  "Illegal context switch in RCU-bh read-side critical section"); \
         RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
                  "Illegal context switch in RCU-sched read-side critical section"); \
     } while (0)
 
 #else /* #ifdef CONFIG_PROVE_RCU */
 
 #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
 #define rcu_sleep_check() do { } while (0)
 
 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 
 /*
  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
  * and rcu_assign_pointer().  Some of these could be folded into their
  * callers, but they are left separate in order to ease introduction of
  * multiple pointers markings to match different RCU implementations
  * (e.g., __srcu), should this make sense in the future.
  */
 
 #ifdef __CHECKER__
 #define rcu_check_sparse(p, space) \
     ((void)(((typeof(*p) space *)p) == p))
 #else /* #ifdef __CHECKER__ */
 #define rcu_check_sparse(p, space)
 #endif /* #else #ifdef __CHECKER__ */
 
 #define __unrcu_pointer(p, local)                   \
 ({                                  \
     typeof(*p) *local = (typeof(*p) *__force)(p);           \
     rcu_check_sparse(p, __rcu);                 \
     ((typeof(*p) __force __kernel *)(local));           \
 })
 /**
  * unrcu_pointer - mark a pointer as not being RCU protected
  * @p: pointer needing to lose its __rcu property
  *
  * Converts @p from an __rcu pointer to a __kernel pointer.
  * This allows an __rcu pointer to be used with xchg() and friends.
  */
 #define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
 
 #define __rcu_access_pointer(p, local, space) \
 ({ \
     typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
     rcu_check_sparse(p, space); \
     ((typeof(*p) __force __kernel *)(local)); \
 })
 #define __rcu_dereference_check(p, local, c, space) \
 ({ \
     /* Dependency order vs. p above. */ \
     typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
     RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
     rcu_check_sparse(p, space); \
     ((typeof(*p) __force __kernel *)(local)); \
 })
 #define __rcu_dereference_protected(p, local, c, space) \
 ({ \
     RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
     rcu_check_sparse(p, space); \
     ((typeof(*p) __force __kernel *)(p)); \
 })
 #define __rcu_dereference_raw(p, local) \
 ({ \
     /* Dependency order vs. p above. */ \
     typeof(p) local = READ_ONCE(p); \
     ((typeof(*p) __force __kernel *)(local)); \
 })
 #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
 
 /**
  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
  * @v: The value to statically initialize with.
  */
 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
 
 /**
  * rcu_assign_pointer() - assign to RCU-protected pointer
  * @p: pointer to assign to
  * @v: value to assign (publish)
  *
  * Assigns the specified value to the specified RCU-protected
  * pointer, ensuring that any concurrent RCU readers will see
  * any prior initialization.
  *
  * Inserts memory barriers on architectures that require them
  * (which is most of them), and also prevents the compiler from
  * reordering the code that initializes the structure after the pointer
  * assignment.  More importantly, this call documents which pointers
  * will be dereferenced by RCU read-side code.
  *
  * In some special cases, you may use RCU_INIT_POINTER() instead
  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
  * to the fact that it does not constrain either the CPU or the compiler.
  * That said, using RCU_INIT_POINTER() when you should have used
  * rcu_assign_pointer() is a very bad thing that results in
  * impossible-to-diagnose memory corruption.  So please be careful.
  * See the RCU_INIT_POINTER() comment header for details.
  *
  * Note that rcu_assign_pointer() evaluates each of its arguments only
  * once, appearances notwithstanding.  One of the "extra" evaluations
  * is in typeof() and the other visible only to sparse (__CHECKER__),
  * neither of which actually execute the argument.  As with most cpp
  * macros, this execute-arguments-only-once property is important, so
  * please be careful when making changes to rcu_assign_pointer() and the
  * other macros that it invokes.
  */
 #define rcu_assign_pointer(p, v)                          \
 do {                                          \
     uintptr_t _r_a_p__v = (uintptr_t)(v);                     \
     rcu_check_sparse(p, __rcu);                       \
                                           \
     if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL)        \
         WRITE_ONCE((p), (typeof(p))(_r_a_p__v));              \
     else                                      \
         smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
 } while (0)
 
 /**
  * rcu_replace_pointer() - replace an RCU pointer, returning its old value
  * @rcu_ptr: RCU pointer, whose old value is returned
  * @ptr: regular pointer
  * @c: the lockdep conditions under which the dereference will take place
  *
  * Perform a replacement, where @rcu_ptr is an RCU-annotated
  * pointer and @c is the lockdep argument that is passed to the
  * rcu_dereference_protected() call used to read that pointer.  The old
  * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
  */
 #define rcu_replace_pointer(rcu_ptr, ptr, c)                \
 ({                                  \
     typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c));  \
     rcu_assign_pointer((rcu_ptr), (ptr));               \
     __tmp;                              \
 })
 
 /**
  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
  * @p: The pointer to read
  *
  * Return the value of the specified RCU-protected pointer, but omit the
  * lockdep checks for being in an RCU read-side critical section.  This is
  * useful when the value of this pointer is accessed, but the pointer is
  * not dereferenced, for example, when testing an RCU-protected pointer
  * against NULL.  Although rcu_access_pointer() may also be used in cases
  * where update-side locks prevent the value of the pointer from changing,
  * you should instead use rcu_dereference_protected() for this use case.
  *
  * It is also permissible to use rcu_access_pointer() when read-side
  * access to the pointer was removed at least one grace period ago, as
  * is the case in the context of the RCU callback that is freeing up
  * the data, or after a synchronize_rcu() returns.  This can be useful
  * when tearing down multi-linked structures after a grace period
  * has elapsed.
  */
 #define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)
 
 /**
  * rcu_dereference_check() - rcu_dereference with debug checking
  * @p: The pointer to read, prior to dereferencing
  * @c: The conditions under which the dereference will take place
  *
  * Do an rcu_dereference(), but check that the conditions under which the
  * dereference will take place are correct.  Typically the conditions
  * indicate the various locking conditions that should be held at that
  * point.  The check should return true if the conditions are satisfied.
  * An implicit check for being in an RCU read-side critical section
  * (rcu_read_lock()) is included.
  *
  * For example:
  *
  *  bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
  *
  * could be used to indicate to lockdep that foo->bar may only be dereferenced
  * if either rcu_read_lock() is held, or that the lock required to replace
  * the bar struct at foo->bar is held.
  *
  * Note that the list of conditions may also include indications of when a lock
  * need not be held, for example during initialisation or destruction of the
  * target struct:
  *
  *  bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
  *                        atomic_read(&foo->usage) == 0);
  *
  * Inserts memory barriers on architectures that require them
  * (currently only the Alpha), prevents the compiler from refetching
  * (and from merging fetches), and, more importantly, documents exactly
  * which pointers are protected by RCU and checks that the pointer is
  * annotated as __rcu.
  */
 #define rcu_dereference_check(p, c) \
     __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
                 (c) || rcu_read_lock_held(), __rcu)
 
 /**
  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
  * @p: The pointer to read, prior to dereferencing
  * @c: The conditions under which the dereference will take place
  *
  * This is the RCU-bh counterpart to rcu_dereference_check().  However,
  * please note that starting in v5.0 kernels, vanilla RCU grace periods
  * wait for local_bh_disable() regions of code in addition to regions of
  * code demarked by rcu_read_lock() and rcu_read_unlock().  This means
  * that synchronize_rcu(), call_rcu, and friends all take not only
  * rcu_read_lock() but also rcu_read_lock_bh() into account.
  */
 #define rcu_dereference_bh_check(p, c) \
     __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
                 (c) || rcu_read_lock_bh_held(), __rcu)
 
 /**
  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
  * @p: The pointer to read, prior to dereferencing
  * @c: The conditions under which the dereference will take place
  *
  * This is the RCU-sched counterpart to rcu_dereference_check().
  * However, please note that starting in v5.0 kernels, vanilla RCU grace
  * periods wait for preempt_disable() regions of code in addition to
  * regions of code demarked by rcu_read_lock() and rcu_read_unlock().
  * This means that synchronize_rcu(), call_rcu, and friends all take not
  * only rcu_read_lock() but also rcu_read_lock_sched() into account.
  */
 #define rcu_dereference_sched_check(p, c) \
     __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
                 (c) || rcu_read_lock_sched_held(), \
                 __rcu)
 
 /*
  * The tracing infrastructure traces RCU (we want that), but unfortunately
  * some of the RCU checks causes tracing to lock up the system.
  *
  * The no-tracing version of rcu_dereference_raw() must not call
  * rcu_read_lock_held().
  */
 #define rcu_dereference_raw_check(p) \
     __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu)
 
 /**
  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
  * @p: The pointer to read, prior to dereferencing
  * @c: The conditions under which the dereference will take place
  *
  * Return the value of the specified RCU-protected pointer, but omit
  * the READ_ONCE().  This is useful in cases where update-side locks
  * prevent the value of the pointer from changing.  Please note that this
  * primitive does *not* prevent the compiler from repeating this reference
  * or combining it with other references, so it should not be used without
  * protection of appropriate locks.
  *
  * This function is only for update-side use.  Using this function
  * when protected only by rcu_read_lock() will result in infrequent
  * but very ugly failures.
  */
 #define rcu_dereference_protected(p, c) \
     __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu)
 
 
 /**
  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
  * @p: The pointer to read, prior to dereferencing
  *
  * This is a simple wrapper around rcu_dereference_check().
  */
 #define rcu_dereference(p) rcu_dereference_check(p, 0)
 
 /**
  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
  * @p: The pointer to read, prior to dereferencing
  *
  * Makes rcu_dereference_check() do the dirty work.
  */
 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
 
 /**
  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
  * @p: The pointer to read, prior to dereferencing
  *
  * Makes rcu_dereference_check() do the dirty work.
  */
 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
 
 /**
  * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
  * @p: The pointer to hand off
  *
  * This is simply an identity function, but it documents where a pointer
  * is handed off from RCU to some other synchronization mechanism, for
  * example, reference counting or locking.  In C11, it would map to
  * kill_dependency().  It could be used as follows::
  *
  *  rcu_read_lock();
  *  p = rcu_dereference(gp);
  *  long_lived = is_long_lived(p);
  *  if (long_lived) {
  *      if (!atomic_inc_not_zero(p->refcnt))
  *          long_lived = false;
  *      else
  *          p = rcu_pointer_handoff(p);
  *  }
  *  rcu_read_unlock();
  */
 #define rcu_pointer_handoff(p) (p)
 
 /**
  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
  *
  * When synchronize_rcu() is invoked on one CPU while other CPUs
  * are within RCU read-side critical sections, then the
  * synchronize_rcu() is guaranteed to block until after all the other
  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
  * on one CPU while other CPUs are within RCU read-side critical
  * sections, invocation of the corresponding RCU callback is deferred
  * until after the all the other CPUs exit their critical sections.
  *
  * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also
  * wait for regions of code with preemption disabled, including regions of
  * code with interrupts or softirqs disabled.  In pre-v5.0 kernels, which
  * define synchronize_sched(), only code enclosed within rcu_read_lock()
  * and rcu_read_unlock() are guaranteed to be waited for.
  *
  * Note, however, that RCU callbacks are permitted to run concurrently
  * with new RCU read-side critical sections.  One way that this can happen
  * is via the following sequence of events: (1) CPU 0 enters an RCU
  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
  * callback is invoked.  This is legal, because the RCU read-side critical
  * section that was running concurrently with the call_rcu() (and which
  * therefore might be referencing something that the corresponding RCU
  * callback would free up) has completed before the corresponding
  * RCU callback is invoked.
  *
  * RCU read-side critical sections may be nested.  Any deferred actions
  * will be deferred until the outermost RCU read-side critical section
  * completes.
  *
  * You can avoid reading and understanding the next paragraph by
  * following this rule: don't put anything in an rcu_read_lock() RCU
  * read-side critical section that would block in a !PREEMPTION kernel.
  * But if you want the full story, read on!
  *
  * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
  * it is illegal to block while in an RCU read-side critical section.
  * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
  * kernel builds, RCU read-side critical sections may be preempted,
  * but explicit blocking is illegal.  Finally, in preemptible RCU
  * implementations in real-time (with -rt patchset) kernel builds, RCU
  * read-side critical sections may be preempted and they may also block, but
  * only when acquiring spinlocks that are subject to priority inheritance.
  */
 static __always_inline void rcu_read_lock(void)
 {
     __rcu_read_lock();
     __acquire(RCU);
     rcu_lock_acquire(&rcu_lock_map);
     RCU_LOCKDEP_WARN(!rcu_is_watching(),
              "rcu_read_lock() used illegally while idle");
 }
 
 /*
  * So where is rcu_write_lock()?  It does not exist, as there is no
  * way for writers to lock out RCU readers.  This is a feature, not
  * a bug -- this property is what provides RCU's performance benefits.
  * Of course, writers must coordinate with each other.  The normal
  * spinlock primitives work well for this, but any other technique may be
  * used as well.  RCU does not care how the writers keep out of each
  * others' way, as long as they do so.
  */
 
 /**
  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
  *
  * In almost all situations, rcu_read_unlock() is immune from deadlock.
  * In recent kernels that have consolidated synchronize_sched() and
  * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity
  * also extends to the scheduler's runqueue and priority-inheritance
  * spinlocks, courtesy of the quiescent-state deferral that is carried
  * out when rcu_read_unlock() is invoked with interrupts disabled.
  *
  * See rcu_read_lock() for more information.
  */
 static inline void rcu_read_unlock(void)
 {
     RCU_LOCKDEP_WARN(!rcu_is_watching(),
              "rcu_read_unlock() used illegally while idle");
     __release(RCU);
     __rcu_read_unlock();
     rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
 }
 
 /**
  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
  *
  * This is equivalent to rcu_read_lock(), but also disables softirqs.
  * Note that anything else that disables softirqs can also serve as an RCU
  * read-side critical section.  However, please note that this equivalence
  * applies only to v5.0 and later.  Before v5.0, rcu_read_lock() and
  * rcu_read_lock_bh() were unrelated.
  *
  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
  * must occur in the same context, for example, it is illegal to invoke
  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
  * was invoked from some other task.
  */
 static inline void rcu_read_lock_bh(void)
 {
     local_bh_disable();
     __acquire(RCU_BH);
     rcu_lock_acquire(&rcu_bh_lock_map);
     RCU_LOCKDEP_WARN(!rcu_is_watching(),
              "rcu_read_lock_bh() used illegally while idle");
 }
 
 /**
  * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
  *
  * See rcu_read_lock_bh() for more information.
  */
 static inline void rcu_read_unlock_bh(void)
 {
     RCU_LOCKDEP_WARN(!rcu_is_watching(),
              "rcu_read_unlock_bh() used illegally while idle");
     rcu_lock_release(&rcu_bh_lock_map);
     __release(RCU_BH);
     local_bh_enable();
 }
 
 /**
  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
  *
  * This is equivalent to rcu_read_lock(), but also disables preemption.
  * Read-side critical sections can also be introduced by anything else that
  * disables preemption, including local_irq_disable() and friends.  However,
  * please note that the equivalence to rcu_read_lock() applies only to
  * v5.0 and later.  Before v5.0, rcu_read_lock() and rcu_read_lock_sched()
  * were unrelated.
  *
  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
  * must occur in the same context, for example, it is illegal to invoke
  * rcu_read_unlock_sched() from process context if the matching
  * rcu_read_lock_sched() was invoked from an NMI handler.
  */
 static inline void rcu_read_lock_sched(void)
 {
     preempt_disable();
     __acquire(RCU_SCHED);
     rcu_lock_acquire(&rcu_sched_lock_map);
     RCU_LOCKDEP_WARN(!rcu_is_watching(),
              "rcu_read_lock_sched() used illegally while idle");
 }
 
 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 static inline notrace void rcu_read_lock_sched_notrace(void)
 {
     preempt_disable_notrace();
     __acquire(RCU_SCHED);
 }
 
 /**
  * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
  *
  * See rcu_read_lock_sched() for more information.
  */
 static inline void rcu_read_unlock_sched(void)
 {
     RCU_LOCKDEP_WARN(!rcu_is_watching(),
              "rcu_read_unlock_sched() used illegally while idle");
     rcu_lock_release(&rcu_sched_lock_map);
     __release(RCU_SCHED);
     preempt_enable();
 }
 
 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
 static inline notrace void rcu_read_unlock_sched_notrace(void)
 {
     __release(RCU_SCHED);
     preempt_enable_notrace();
 }
 
 /**
  * RCU_INIT_POINTER() - initialize an RCU protected pointer
  * @p: The pointer to be initialized.
  * @v: The value to initialized the pointer to.
  *
  * Initialize an RCU-protected pointer in special cases where readers
  * do not need ordering constraints on the CPU or the compiler.  These
  * special cases are:
  *
  * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
  * 2.   The caller has taken whatever steps are required to prevent
  *  RCU readers from concurrently accessing this pointer *or*
  * 3.   The referenced data structure has already been exposed to
  *  readers either at compile time or via rcu_assign_pointer() *and*
  *
  *  a.  You have not made *any* reader-visible changes to
  *      this structure since then *or*
  *  b.  It is OK for readers accessing this structure from its
  *      new location to see the old state of the structure.  (For
  *      example, the changes were to statistical counters or to
  *      other state where exact synchronization is not required.)
  *
  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
  * result in impossible-to-diagnose memory corruption.  As in the structures
  * will look OK in crash dumps, but any concurrent RCU readers might
  * see pre-initialized values of the referenced data structure.  So
  * please be very careful how you use RCU_INIT_POINTER()!!!
  *
  * If you are creating an RCU-protected linked structure that is accessed
  * by a single external-to-structure RCU-protected pointer, then you may
  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
  * pointers, but you must use rcu_assign_pointer() to initialize the
  * external-to-structure pointer *after* you have completely initialized
  * the reader-accessible portions of the linked structure.
  *
  * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
  * ordering guarantees for either the CPU or the compiler.
  */
 #define RCU_INIT_POINTER(p, v) \
     do { \
         rcu_check_sparse(p, __rcu); \
         WRITE_ONCE(p, RCU_INITIALIZER(v)); \
     } while (0)
 
 /**
  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
  * @p: The pointer to be initialized.
  * @v: The value to initialized the pointer to.
  *
  * GCC-style initialization for an RCU-protected pointer in a structure field.
  */
 #define RCU_POINTER_INITIALIZER(p, v) \
         .p = RCU_INITIALIZER(v)
 
 /*
  * Does the specified offset indicate that the corresponding rcu_head
  * structure can be handled by kvfree_rcu()?
  */
 #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
 
 /**
  * kfree_rcu() - kfree an object after a grace period.
  * @ptr: pointer to kfree for both single- and double-argument invocations.
  * @rhf: the name of the struct rcu_head within the type of @ptr,
  *       but only for double-argument invocations.
  *
  * Many rcu callbacks functions just call kfree() on the base structure.
  * These functions are trivial, but their size adds up, and furthermore
  * when they are used in a kernel module, that module must invoke the
  * high-latency rcu_barrier() function at module-unload time.
  *
  * The kfree_rcu() function handles this issue.  Rather than encoding a
  * function address in the embedded rcu_head structure, kfree_rcu() instead
  * encodes the offset of the rcu_head structure within the base structure.
  * Because the functions are not allowed in the low-order 4096 bytes of
  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
  * If the offset is larger than 4095 bytes, a compile-time error will
  * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
  * either fall back to use of call_rcu() or rearrange the structure to
  * position the rcu_head structure into the first 4096 bytes.
  *
  * Note that the allowable offset might decrease in the future, for example,
  * to allow something like kmem_cache_free_rcu().
  *
  * The BUILD_BUG_ON check must not involve any function calls, hence the
  * checks are done in macros here.
  */
 #define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf)
 
 /**
  * kvfree_rcu() - kvfree an object after a grace period.
  *
  * This macro consists of one or two arguments and it is
  * based on whether an object is head-less or not. If it
  * has a head then a semantic stays the same as it used
  * to be before:
  *
  *     kvfree_rcu(ptr, rhf);
  *
  * where @ptr is a pointer to kvfree(), @rhf is the name
  * of the rcu_head structure within the type of @ptr.
  *
  * When it comes to head-less variant, only one argument
  * is passed and that is just a pointer which has to be
  * freed after a grace period. Therefore the semantic is
  *
  *     kvfree_rcu(ptr);
  *
  * where @ptr is the pointer to be freed by kvfree().
  *
  * Please note, head-less way of freeing is permitted to
  * use from a context that has to follow might_sleep()
  * annotation. Otherwise, please switch and embed the
  * rcu_head structure within the type of @ptr.
  */
 #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__,       \
     kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
 
 #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
 #define kvfree_rcu_arg_2(ptr, rhf)                  \
 do {                                    \
     typeof (ptr) ___p = (ptr);                  \
                                     \
     if (___p) {                                 \
         BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf)));   \
         kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long)     \
             (offsetof(typeof(*(ptr)), rhf)));               \
     }                                       \
 } while (0)
 
 #define kvfree_rcu_arg_1(ptr)                   \
 do {                                \
     typeof(ptr) ___p = (ptr);               \
                                 \
     if (___p)                       \
         kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \
 } while (0)
 
 /*
  * Place this after a lock-acquisition primitive to guarantee that
  * an UNLOCK+LOCK pair acts as a full barrier.  This guarantee applies
  * if the UNLOCK and LOCK are executed by the same CPU or if the
  * UNLOCK and LOCK operate on the same lock variable.
  */
 #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
 #define smp_mb__after_unlock_lock() smp_mb()  /* Full ordering for lock. */
 #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
 #define smp_mb__after_unlock_lock() do { } while (0)
 #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
 
 
 /* Has the specified rcu_head structure been handed to call_rcu()? */
 
 /**
  * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
  * @rhp: The rcu_head structure to initialize.
  *
  * If you intend to invoke rcu_head_after_call_rcu() to test whether a
  * given rcu_head structure has already been passed to call_rcu(), then
  * you must also invoke this rcu_head_init() function on it just after
  * allocating that structure.  Calls to this function must not race with
  * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
  */
 static inline void rcu_head_init(struct rcu_head *rhp)
 {
     rhp->func = (rcu_callback_t)~0L;
 }
 
 /**
  * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
  * @rhp: The rcu_head structure to test.
  * @f: The function passed to call_rcu() along with @rhp.
  *
  * Returns @true if the @rhp has been passed to call_rcu() with @func,
  * and @false otherwise.  Emits a warning in any other case, including
  * the case where @rhp has already been invoked after a grace period.
  * Calls to this function must not race with callback invocation.  One way
  * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
  * in an RCU read-side critical section that includes a read-side fetch
  * of the pointer to the structure containing @rhp.
  */
 static inline bool
 rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
 {
     rcu_callback_t func = READ_ONCE(rhp->func);
 
     if (func == f)
         return true;
     WARN_ON_ONCE(func != (rcu_callback_t)~0L);
     return false;
 }
 
 /* kernel/ksysfs.c definitions */
 extern int rcu_expedited;
 extern int rcu_normal;
 
 #endif /* __LINUX_RCUPDATE_H */

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