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 // SPDX-License-Identifier: GPL-2.0
 /*
  * KCSAN core runtime.
  *
  * Copyright (C) 2019, Google LLC.
  */
 
 #define pr_fmt(fmt) "kcsan: " fmt
 
 #include <linux/atomic.h>
 #include <linux/bug.h>
 #include <linux/delay.h>
 #include <linux/export.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/moduleparam.h>
 #include <linux/percpu.h>
 #include <linux/preempt.h>
 #include <linux/sched.h>
 #include <linux/uaccess.h>
 
 #include "encoding.h"
 #include "kcsan.h"
 #include "permissive.h"
 
 static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
 unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
 unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
 static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
 static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
 
 #ifdef MODULE_PARAM_PREFIX
 #undef MODULE_PARAM_PREFIX
 #endif
 #define MODULE_PARAM_PREFIX "kcsan."
 module_param_named(early_enable, kcsan_early_enable, bool, 0);
 module_param_named(udelay_task, kcsan_udelay_task, uint, 0644);
 module_param_named(udelay_interrupt, kcsan_udelay_interrupt, uint, 0644);
 module_param_named(skip_watch, kcsan_skip_watch, long, 0644);
 module_param_named(interrupt_watcher, kcsan_interrupt_watcher, bool, 0444);
 
 #ifdef CONFIG_KCSAN_WEAK_MEMORY
 static bool kcsan_weak_memory = true;
 module_param_named(weak_memory, kcsan_weak_memory, bool, 0644);
 #else
 #define kcsan_weak_memory false
 #endif
 
 bool kcsan_enabled;
 
 /* Per-CPU kcsan_ctx for interrupts */
 static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = {
     .scoped_accesses    = {LIST_POISON1, NULL},
 };
 
 /*
  * Helper macros to index into adjacent slots, starting from address slot
  * itself, followed by the right and left slots.
  *
  * The purpose is 2-fold:
  *
  *  1. if during insertion the address slot is already occupied, check if
  *     any adjacent slots are free;
  *  2. accesses that straddle a slot boundary due to size that exceeds a
  *     slot's range may check adjacent slots if any watchpoint matches.
  *
  * Note that accesses with very large size may still miss a watchpoint; however,
  * given this should be rare, this is a reasonable trade-off to make, since this
  * will avoid:
  *
  *  1. excessive contention between watchpoint checks and setup;
  *  2. larger number of simultaneous watchpoints without sacrificing
  *     performance.
  *
  * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]:
  *
  *   slot=0:  [ 1,  2,  0]
  *   slot=9:  [10, 11,  9]
  *   slot=63: [64, 65, 63]
  */
 #define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS))
 
 /*
  * SLOT_IDX_FAST is used in the fast-path. Not first checking the address's primary
  * slot (middle) is fine if we assume that races occur rarely. The set of
  * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to
  * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}.
  */
 #define SLOT_IDX_FAST(slot, i) (slot + i)
 
 /*
  * Watchpoints, with each entry encoded as defined in encoding.h: in order to be
  * able to safely update and access a watchpoint without introducing locking
  * overhead, we encode each watchpoint as a single atomic long. The initial
  * zero-initialized state matches INVALID_WATCHPOINT.
  *
  * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to
  * use more complicated SLOT_IDX_FAST calculation with modulo in the fast-path.
  */
 static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1];
 
 /*
  * Instructions to skip watching counter, used in should_watch(). We use a
  * per-CPU counter to avoid excessive contention.
  */
 static DEFINE_PER_CPU(long, kcsan_skip);
 
 /* For kcsan_prandom_u32_max(). */
 static DEFINE_PER_CPU(u32, kcsan_rand_state);
 
 static __always_inline atomic_long_t *find_watchpoint(unsigned long addr,
                               size_t size,
                               bool expect_write,
                               long *encoded_watchpoint)
 {
     const int slot = watchpoint_slot(addr);
     const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK;
     atomic_long_t *watchpoint;
     unsigned long wp_addr_masked;
     size_t wp_size;
     bool is_write;
     int i;
 
     BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS);
 
     for (i = 0; i < NUM_SLOTS; ++i) {
         watchpoint = &watchpoints[SLOT_IDX_FAST(slot, i)];
         *encoded_watchpoint = atomic_long_read(watchpoint);
         if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked,
                        &wp_size, &is_write))
             continue;
 
         if (expect_write && !is_write)
             continue;
 
         /* Check if the watchpoint matches the access. */
         if (matching_access(wp_addr_masked, wp_size, addr_masked, size))
             return watchpoint;
     }
 
     return NULL;
 }
 
 static inline atomic_long_t *
 insert_watchpoint(unsigned long addr, size_t size, bool is_write)
 {
     const int slot = watchpoint_slot(addr);
     const long encoded_watchpoint = encode_watchpoint(addr, size, is_write);
     atomic_long_t *watchpoint;
     int i;
 
     /* Check slot index logic, ensuring we stay within array bounds. */
     BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT);
     BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT+1) != 0);
     BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT) != ARRAY_SIZE(watchpoints)-1);
     BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT+1) != ARRAY_SIZE(watchpoints) - NUM_SLOTS);
 
     for (i = 0; i < NUM_SLOTS; ++i) {
         long expect_val = INVALID_WATCHPOINT;
 
         /* Try to acquire this slot. */
         watchpoint = &watchpoints[SLOT_IDX(slot, i)];
         if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val, encoded_watchpoint))
             return watchpoint;
     }
 
     return NULL;
 }
 
 /*
  * Return true if watchpoint was successfully consumed, false otherwise.
  *
  * This may return false if:
  *
  *  1. another thread already consumed the watchpoint;
  *  2. the thread that set up the watchpoint already removed it;
  *  3. the watchpoint was removed and then re-used.
  */
 static __always_inline bool
 try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint)
 {
     return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint, CONSUMED_WATCHPOINT);
 }
 
 /* Return true if watchpoint was not touched, false if already consumed. */
 static inline bool consume_watchpoint(atomic_long_t *watchpoint)
 {
     return atomic_long_xchg_relaxed(watchpoint, CONSUMED_WATCHPOINT) != CONSUMED_WATCHPOINT;
 }
 
 /* Remove the watchpoint -- its slot may be reused after. */
 static inline void remove_watchpoint(atomic_long_t *watchpoint)
 {
     atomic_long_set(watchpoint, INVALID_WATCHPOINT);
 }
 
 static __always_inline struct kcsan_ctx *get_ctx(void)
 {
     /*
      * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would
      * also result in calls that generate warnings in uaccess regions.
      */
     return in_task() ? &current->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
 }
 
 static __always_inline void
 check_access(const volatile void *ptr, size_t size, int type, unsigned long ip);
 
 /* Check scoped accesses; never inline because this is a slow-path! */
 static noinline void kcsan_check_scoped_accesses(void)
 {
     struct kcsan_ctx *ctx = get_ctx();
     struct kcsan_scoped_access *scoped_access;
 
     if (ctx->disable_scoped)
         return;
 
     ctx->disable_scoped++;
     list_for_each_entry(scoped_access, &ctx->scoped_accesses, list) {
         check_access(scoped_access->ptr, scoped_access->size,
                  scoped_access->type, scoped_access->ip);
     }
     ctx->disable_scoped--;
 }
 
 /* Rules for generic atomic accesses. Called from fast-path. */
 static __always_inline bool
 is_atomic(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type)
 {
     if (type & KCSAN_ACCESS_ATOMIC)
         return true;
 
     /*
      * Unless explicitly declared atomic, never consider an assertion access
      * as atomic. This allows using them also in atomic regions, such as
      * seqlocks, without implicitly changing their semantics.
      */
     if (type & KCSAN_ACCESS_ASSERT)
         return false;
 
     if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) &&
         (type & KCSAN_ACCESS_WRITE) && size <= sizeof(long) &&
         !(type & KCSAN_ACCESS_COMPOUND) && IS_ALIGNED((unsigned long)ptr, size))
         return true; /* Assume aligned writes up to word size are atomic. */
 
     if (ctx->atomic_next > 0) {
         /*
          * Because we do not have separate contexts for nested
          * interrupts, in case atomic_next is set, we simply assume that
          * the outer interrupt set atomic_next. In the worst case, we
          * will conservatively consider operations as atomic. This is a
          * reasonable trade-off to make, since this case should be
          * extremely rare; however, even if extremely rare, it could
          * lead to false positives otherwise.
          */
         if ((hardirq_count() >> HARDIRQ_SHIFT) < 2)
             --ctx->atomic_next; /* in task, or outer interrupt */
         return true;
     }
 
     return ctx->atomic_nest_count > 0 || ctx->in_flat_atomic;
 }
 
 static __always_inline bool
 should_watch(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type)
 {
     /*
      * Never set up watchpoints when memory operations are atomic.
      *
      * Need to check this first, before kcsan_skip check below: (1) atomics
      * should not count towards skipped instructions, and (2) to actually
      * decrement kcsan_atomic_next for consecutive instruction stream.
      */
     if (is_atomic(ctx, ptr, size, type))
         return false;
 
     if (this_cpu_dec_return(kcsan_skip) >= 0)
         return false;
 
     /*
      * NOTE: If we get here, kcsan_skip must always be reset in slow path
      * via reset_kcsan_skip() to avoid underflow.
      */
 
     /* this operation should be watched */
     return true;
 }
 
 /*
  * Returns a pseudo-random number in interval [0, ep_ro). Simple linear
  * congruential generator, using constants from "Numerical Recipes".
  */
 static u32 kcsan_prandom_u32_max(u32 ep_ro)
 {
     u32 state = this_cpu_read(kcsan_rand_state);
 
     state = 1664525 * state + 1013904223;
     this_cpu_write(kcsan_rand_state, state);
 
     return state % ep_ro;
 }
 
 static inline void reset_kcsan_skip(void)
 {
     long skip_count = kcsan_skip_watch -
               (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ?
                    kcsan_prandom_u32_max(kcsan_skip_watch) :
                    0);
     this_cpu_write(kcsan_skip, skip_count);
 }
 
 static __always_inline bool kcsan_is_enabled(struct kcsan_ctx *ctx)
 {
     return READ_ONCE(kcsan_enabled) && !ctx->disable_count;
 }
 
 /* Introduce delay depending on context and configuration. */
 static void delay_access(int type)
 {
     unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt;
     /* For certain access types, skew the random delay to be longer. */
     unsigned int skew_delay_order =
         (type & (KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_ASSERT)) ? 1 : 0;
 
     delay -= IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
                    kcsan_prandom_u32_max(delay >> skew_delay_order) :
                    0;
     udelay(delay);
 }
 
 /*
  * Reads the instrumented memory for value change detection; value change
  * detection is currently done for accesses up to a size of 8 bytes.
  */
 static __always_inline u64 read_instrumented_memory(const volatile void *ptr, size_t size)
 {
     switch (size) {
     case 1:  return READ_ONCE(*(const u8 *)ptr);
     case 2:  return READ_ONCE(*(const u16 *)ptr);
     case 4:  return READ_ONCE(*(const u32 *)ptr);
     case 8:  return READ_ONCE(*(const u64 *)ptr);
     default: return 0; /* Ignore; we do not diff the values. */
     }
 }
 
 void kcsan_save_irqtrace(struct task_struct *task)
 {
 #ifdef CONFIG_TRACE_IRQFLAGS
     task->kcsan_save_irqtrace = task->irqtrace;
 #endif
 }
 
 void kcsan_restore_irqtrace(struct task_struct *task)
 {
 #ifdef CONFIG_TRACE_IRQFLAGS
     task->irqtrace = task->kcsan_save_irqtrace;
 #endif
 }
 
 static __always_inline int get_kcsan_stack_depth(void)
 {
 #ifdef CONFIG_KCSAN_WEAK_MEMORY
     return current->kcsan_stack_depth;
 #else
     BUILD_BUG();
     return 0;
 #endif
 }
 
 static __always_inline void add_kcsan_stack_depth(int val)
 {
 #ifdef CONFIG_KCSAN_WEAK_MEMORY
     current->kcsan_stack_depth += val;
 #else
     BUILD_BUG();
 #endif
 }
 
 static __always_inline struct kcsan_scoped_access *get_reorder_access(struct kcsan_ctx *ctx)
 {
 #ifdef CONFIG_KCSAN_WEAK_MEMORY
     return ctx->disable_scoped ? NULL : &ctx->reorder_access;
 #else
     return NULL;
 #endif
 }
 
 static __always_inline bool
 find_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size,
             int type, unsigned long ip)
 {
     struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
 
     if (!reorder_access)
         return false;
 
     /*
      * Note: If accesses are repeated while reorder_access is identical,
      * never matches the new access, because !(type & KCSAN_ACCESS_SCOPED).
      */
     return reorder_access->ptr == ptr && reorder_access->size == size &&
            reorder_access->type == type && reorder_access->ip == ip;
 }
 
 static inline void
 set_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size,
            int type, unsigned long ip)
 {
     struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
 
     if (!reorder_access || !kcsan_weak_memory)
         return;
 
     /*
      * To avoid nested interrupts or scheduler (which share kcsan_ctx)
      * reading an inconsistent reorder_access, ensure that the below has
      * exclusive access to reorder_access by disallowing concurrent use.
      */
     ctx->disable_scoped++;
     barrier();
     reorder_access->ptr     = ptr;
     reorder_access->size        = size;
     reorder_access->type        = type | KCSAN_ACCESS_SCOPED;
     reorder_access->ip      = ip;
     reorder_access->stack_depth = get_kcsan_stack_depth();
     barrier();
     ctx->disable_scoped--;
 }
 
 /*
  * Pull everything together: check_access() below contains the performance
  * critical operations; the fast-path (including check_access) functions should
  * all be inlinable by the instrumentation functions.
  *
  * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are
  * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can
  * be filtered from the stacktrace, as well as give them unique names for the
  * UACCESS whitelist of objtool. Each function uses user_access_save/restore(),
  * since they do not access any user memory, but instrumentation is still
  * emitted in UACCESS regions.
  */
 
 static noinline void kcsan_found_watchpoint(const volatile void *ptr,
                         size_t size,
                         int type,
                         unsigned long ip,
                         atomic_long_t *watchpoint,
                         long encoded_watchpoint)
 {
     const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;
     struct kcsan_ctx *ctx = get_ctx();
     unsigned long flags;
     bool consumed;
 
     /*
      * We know a watchpoint exists. Let's try to keep the race-window
      * between here and finally consuming the watchpoint below as small as
      * possible -- avoid unneccessarily complex code until consumed.
      */
 
     if (!kcsan_is_enabled(ctx))
         return;
 
     /*
      * The access_mask check relies on value-change comparison. To avoid
      * reporting a race where e.g. the writer set up the watchpoint, but the
      * reader has access_mask!=0, we have to ignore the found watchpoint.
      *
      * reorder_access is never created from an access with access_mask set.
      */
     if (ctx->access_mask && !find_reorder_access(ctx, ptr, size, type, ip))
         return;
 
     /*
      * If the other thread does not want to ignore the access, and there was
      * a value change as a result of this thread's operation, we will still
      * generate a report of unknown origin.
      *
      * Use CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n to filter.
      */
     if (!is_assert && kcsan_ignore_address(ptr))
         return;
 
     /*
      * Consuming the watchpoint must be guarded by kcsan_is_enabled() to
      * avoid erroneously triggering reports if the context is disabled.
      */
     consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint);
 
     /* keep this after try_consume_watchpoint */
     flags = user_access_save();
 
     if (consumed) {
         kcsan_save_irqtrace(current);
         kcsan_report_set_info(ptr, size, type, ip, watchpoint - watchpoints);
         kcsan_restore_irqtrace(current);
     } else {
         /*
          * The other thread may not print any diagnostics, as it has
          * already removed the watchpoint, or another thread consumed
          * the watchpoint before this thread.
          */
         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_REPORT_RACES]);
     }
 
     if (is_assert)
         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
     else
         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_DATA_RACES]);
 
     user_access_restore(flags);
 }
 
 static noinline void
 kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned long ip)
 {
     const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
     const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;
     atomic_long_t *watchpoint;
     u64 old, new, diff;
     enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE;
     bool interrupt_watcher = kcsan_interrupt_watcher;
     unsigned long ua_flags = user_access_save();
     struct kcsan_ctx *ctx = get_ctx();
     unsigned long access_mask = ctx->access_mask;
     unsigned long irq_flags = 0;
     bool is_reorder_access;
 
     /*
      * Always reset kcsan_skip counter in slow-path to avoid underflow; see
      * should_watch().
      */
     reset_kcsan_skip();
 
     if (!kcsan_is_enabled(ctx))
         goto out;
 
     /*
      * Check to-ignore addresses after kcsan_is_enabled(), as we may access
      * memory that is not yet initialized during early boot.
      */
     if (!is_assert && kcsan_ignore_address(ptr))
         goto out;
 
     if (!check_encodable((unsigned long)ptr, size)) {
         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]);
         goto out;
     }
 
     /*
      * The local CPU cannot observe reordering of its own accesses, and
      * therefore we need to take care of 2 cases to avoid false positives:
      *
      *  1. Races of the reordered access with interrupts. To avoid, if
      *     the current access is reorder_access, disable interrupts.
      *  2. Avoid races of scoped accesses from nested interrupts (below).
      */
     is_reorder_access = find_reorder_access(ctx, ptr, size, type, ip);
     if (is_reorder_access)
         interrupt_watcher = false;
     /*
      * Avoid races of scoped accesses from nested interrupts (or scheduler).
      * Assume setting up a watchpoint for a non-scoped (normal) access that
      * also conflicts with a current scoped access. In a nested interrupt,
      * which shares the context, it would check a conflicting scoped access.
      * To avoid, disable scoped access checking.
      */
     ctx->disable_scoped++;
 
     /*
      * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's
      * runtime is entered for every memory access, and potentially useful
      * information is lost if dirtied by KCSAN.
      */
     kcsan_save_irqtrace(current);
     if (!interrupt_watcher)
         local_irq_save(irq_flags);
 
     watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
     if (watchpoint == NULL) {
         /*
          * Out of capacity: the size of 'watchpoints', and the frequency
          * with which should_watch() returns true should be tweaked so
          * that this case happens very rarely.
          */
         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]);
         goto out_unlock;
     }
 
     atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]);
     atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);
 
     /*
      * Read the current value, to later check and infer a race if the data
      * was modified via a non-instrumented access, e.g. from a device.
      */
     old = is_reorder_access ? 0 : read_instrumented_memory(ptr, size);
 
     /*
      * Delay this thread, to increase probability of observing a racy
      * conflicting access.
      */
     delay_access(type);
 
     /*
      * Re-read value, and check if it is as expected; if not, we infer a
      * racy access.
      */
     if (!is_reorder_access) {
         new = read_instrumented_memory(ptr, size);
     } else {
         /*
          * Reordered accesses cannot be used for value change detection,
          * because the memory location may no longer be accessible and
          * could result in a fault.
          */
         new = 0;
         access_mask = 0;
     }
 
     diff = old ^ new;
     if (access_mask)
         diff &= access_mask;
 
     /*
      * Check if we observed a value change.
      *
      * Also check if the data race should be ignored (the rules depend on
      * non-zero diff); if it is to be ignored, the below rules for
      * KCSAN_VALUE_CHANGE_MAYBE apply.
      */
     if (diff && !kcsan_ignore_data_race(size, type, old, new, diff))
         value_change = KCSAN_VALUE_CHANGE_TRUE;
 
     /* Check if this access raced with another. */
     if (!consume_watchpoint(watchpoint)) {
         /*
          * Depending on the access type, map a value_change of MAYBE to
          * TRUE (always report) or FALSE (never report).
          */
         if (value_change == KCSAN_VALUE_CHANGE_MAYBE) {
             if (access_mask != 0) {
                 /*
                  * For access with access_mask, we require a
                  * value-change, as it is likely that races on
                  * ~access_mask bits are expected.
                  */
                 value_change = KCSAN_VALUE_CHANGE_FALSE;
             } else if (size > 8 || is_assert) {
                 /* Always assume a value-change. */
                 value_change = KCSAN_VALUE_CHANGE_TRUE;
             }
         }
 
         /*
          * No need to increment 'data_races' counter, as the racing
          * thread already did.
          *
          * Count 'assert_failures' for each failed ASSERT access,
          * therefore both this thread and the racing thread may
          * increment this counter.
          */
         if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
             atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
 
         kcsan_report_known_origin(ptr, size, type, ip,
                       value_change, watchpoint - watchpoints,
                       old, new, access_mask);
     } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {
         /* Inferring a race, since the value should not have changed. */
 
         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]);
         if (is_assert)
             atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
 
         if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert) {
             kcsan_report_unknown_origin(ptr, size, type, ip,
                             old, new, access_mask);
         }
     }
 
     /*
      * Remove watchpoint; must be after reporting, since the slot may be
      * reused after this point.
      */
     remove_watchpoint(watchpoint);
     atomic_long_dec(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);
 
 out_unlock:
     if (!interrupt_watcher)
         local_irq_restore(irq_flags);
     kcsan_restore_irqtrace(current);
     ctx->disable_scoped--;
 
     /*
      * Reordered accesses cannot be used for value change detection,
      * therefore never consider for reordering if access_mask is set.
      * ASSERT_EXCLUSIVE are not real accesses, ignore them as well.
      */
     if (!access_mask && !is_assert)
         set_reorder_access(ctx, ptr, size, type, ip);
 out:
     user_access_restore(ua_flags);
 }
 
 static __always_inline void
 check_access(const volatile void *ptr, size_t size, int type, unsigned long ip)
 {
     atomic_long_t *watchpoint;
     long encoded_watchpoint;
 
     /*
      * Do nothing for 0 sized check; this comparison will be optimized out
      * for constant sized instrumentation (__tsan_{read,write}N).
      */
     if (unlikely(size == 0))
         return;
 
 again:
     /*
      * Avoid user_access_save in fast-path: find_watchpoint is safe without
      * user_access_save, as the address that ptr points to is only used to
      * check if a watchpoint exists; ptr is never dereferenced.
      */
     watchpoint = find_watchpoint((unsigned long)ptr, size,
                      !(type & KCSAN_ACCESS_WRITE),
                      &encoded_watchpoint);
     /*
      * It is safe to check kcsan_is_enabled() after find_watchpoint in the
      * slow-path, as long as no state changes that cause a race to be
      * detected and reported have occurred until kcsan_is_enabled() is
      * checked.
      */
 
     if (unlikely(watchpoint != NULL))
         kcsan_found_watchpoint(ptr, size, type, ip, watchpoint, encoded_watchpoint);
     else {
         struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */
 
         if (unlikely(should_watch(ctx, ptr, size, type))) {
             kcsan_setup_watchpoint(ptr, size, type, ip);
             return;
         }
 
         if (!(type & KCSAN_ACCESS_SCOPED)) {
             struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
 
             if (reorder_access) {
                 /*
                  * reorder_access check: simulates reordering of
                  * the access after subsequent operations.
                  */
                 ptr = reorder_access->ptr;
                 type = reorder_access->type;
                 ip = reorder_access->ip;
                 /*
                  * Upon a nested interrupt, this context's
                  * reorder_access can be modified (shared ctx).
                  * We know that upon return, reorder_access is
                  * always invalidated by setting size to 0 via
                  * __tsan_func_exit(). Therefore we must read
                  * and check size after the other fields.
                  */
                 barrier();
                 size = READ_ONCE(reorder_access->size);
                 if (size)
                     goto again;
             }
         }
 
         /*
          * Always checked last, right before returning from runtime;
          * if reorder_access is valid, checked after it was checked.
          */
         if (unlikely(ctx->scoped_accesses.prev))
             kcsan_check_scoped_accesses();
     }
 }
 
 /* === Public interface ===================================================== */
 
 void __init kcsan_init(void)
 {
     int cpu;
 
     BUG_ON(!in_task());
 
     for_each_possible_cpu(cpu)
         per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles();
 
     /*
      * We are in the init task, and no other tasks should be running;
      * WRITE_ONCE without memory barrier is sufficient.
      */
     if (kcsan_early_enable) {
         pr_info("enabled early\n");
         WRITE_ONCE(kcsan_enabled, true);
     }
 
     if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) ||
         IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) ||
         IS_ENABLED(CONFIG_KCSAN_PERMISSIVE) ||
         IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {
         pr_warn("non-strict mode configured - use CONFIG_KCSAN_STRICT=y to see all data races\n");
     } else {
         pr_info("strict mode configured\n");
     }
 }
 
 /* === Exported interface =================================================== */
 
 void kcsan_disable_current(void)
 {
     ++get_ctx()->disable_count;
 }
 EXPORT_SYMBOL(kcsan_disable_current);
 
 void kcsan_enable_current(void)
 {
     if (get_ctx()->disable_count-- == 0) {
         /*
          * Warn if kcsan_enable_current() calls are unbalanced with
          * kcsan_disable_current() calls, which causes disable_count to
          * become negative and should not happen.
          */
         kcsan_disable_current(); /* restore to 0, KCSAN still enabled */
         kcsan_disable_current(); /* disable to generate warning */
         WARN(1, "Unbalanced %s()", __func__);
         kcsan_enable_current();
     }
 }
 EXPORT_SYMBOL(kcsan_enable_current);
 
 void kcsan_enable_current_nowarn(void)
 {
     if (get_ctx()->disable_count-- == 0)
         kcsan_disable_current();
 }
 EXPORT_SYMBOL(kcsan_enable_current_nowarn);
 
 void kcsan_nestable_atomic_begin(void)
 {
     /*
      * Do *not* check and warn if we are in a flat atomic region: nestable
      * and flat atomic regions are independent from each other.
      * See include/linux/kcsan.h: struct kcsan_ctx comments for more
      * comments.
      */
 
     ++get_ctx()->atomic_nest_count;
 }
 EXPORT_SYMBOL(kcsan_nestable_atomic_begin);
 
 void kcsan_nestable_atomic_end(void)
 {
     if (get_ctx()->atomic_nest_count-- == 0) {
         /*
          * Warn if kcsan_nestable_atomic_end() calls are unbalanced with
          * kcsan_nestable_atomic_begin() calls, which causes
          * atomic_nest_count to become negative and should not happen.
          */
         kcsan_nestable_atomic_begin(); /* restore to 0 */
         kcsan_disable_current(); /* disable to generate warning */
         WARN(1, "Unbalanced %s()", __func__);
         kcsan_enable_current();
     }
 }
 EXPORT_SYMBOL(kcsan_nestable_atomic_end);
 
 void kcsan_flat_atomic_begin(void)
 {
     get_ctx()->in_flat_atomic = true;
 }
 EXPORT_SYMBOL(kcsan_flat_atomic_begin);
 
 void kcsan_flat_atomic_end(void)
 {
     get_ctx()->in_flat_atomic = false;
 }
 EXPORT_SYMBOL(kcsan_flat_atomic_end);
 
 void kcsan_atomic_next(int n)
 {
     get_ctx()->atomic_next = n;
 }
 EXPORT_SYMBOL(kcsan_atomic_next);
 
 void kcsan_set_access_mask(unsigned long mask)
 {
     get_ctx()->access_mask = mask;
 }
 EXPORT_SYMBOL(kcsan_set_access_mask);
 
 struct kcsan_scoped_access *
 kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type,
               struct kcsan_scoped_access *sa)
 {
     struct kcsan_ctx *ctx = get_ctx();
 
     check_access(ptr, size, type, _RET_IP_);
 
     ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
 
     INIT_LIST_HEAD(&sa->list);
     sa->ptr = ptr;
     sa->size = size;
     sa->type = type;
     sa->ip = _RET_IP_;
 
     if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */
         INIT_LIST_HEAD(&ctx->scoped_accesses);
     list_add(&sa->list, &ctx->scoped_accesses);
 
     ctx->disable_count--;
     return sa;
 }
 EXPORT_SYMBOL(kcsan_begin_scoped_access);
 
 void kcsan_end_scoped_access(struct kcsan_scoped_access *sa)
 {
     struct kcsan_ctx *ctx = get_ctx();
 
     if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__))
         return;
 
     ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
 
     list_del(&sa->list);
     if (list_empty(&ctx->scoped_accesses))
         /*
          * Ensure we do not enter kcsan_check_scoped_accesses()
          * slow-path if unnecessary, and avoids requiring list_empty()
          * in the fast-path (to avoid a READ_ONCE() and potential
          * uaccess warning).
          */
         ctx->scoped_accesses.prev = NULL;
 
     ctx->disable_count--;
 
     check_access(sa->ptr, sa->size, sa->type, sa->ip);
 }
 EXPORT_SYMBOL(kcsan_end_scoped_access);
 
 void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
 {
     check_access(ptr, size, type, _RET_IP_);
 }
 EXPORT_SYMBOL(__kcsan_check_access);
 
 #define DEFINE_MEMORY_BARRIER(name, order_before_cond)              \
     void __kcsan_##name(void)                       \
     {                                   \
         struct kcsan_scoped_access *sa = get_reorder_access(get_ctx()); \
         if (!sa)                            \
             return;                         \
         if (order_before_cond)                      \
             sa->size = 0;                       \
     }                                   \
     EXPORT_SYMBOL(__kcsan_##name)
 
 DEFINE_MEMORY_BARRIER(mb, true);
 DEFINE_MEMORY_BARRIER(wmb, sa->type & (KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND));
 DEFINE_MEMORY_BARRIER(rmb, !(sa->type & KCSAN_ACCESS_WRITE) || (sa->type & KCSAN_ACCESS_COMPOUND));
 DEFINE_MEMORY_BARRIER(release, true);
 
 /*
  * KCSAN uses the same instrumentation that is emitted by supported compilers
  * for ThreadSanitizer (TSAN).
  *
  * When enabled, the compiler emits instrumentation calls (the functions
  * prefixed with "__tsan" below) for all loads and stores that it generated;
  * inline asm is not instrumented.
  *
  * Note that, not all supported compiler versions distinguish aligned/unaligned
  * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned
  * version to the generic version, which can handle both.
  */
 
 #define DEFINE_TSAN_READ_WRITE(size)                                           \
     void __tsan_read##size(void *ptr);                                     \
     void __tsan_read##size(void *ptr)                                      \
     {                                                                      \
         check_access(ptr, size, 0, _RET_IP_);                          \
     }                                                                      \
     EXPORT_SYMBOL(__tsan_read##size);                                      \
     void __tsan_unaligned_read##size(void *ptr)                            \
         __alias(__tsan_read##size);                                    \
     EXPORT_SYMBOL(__tsan_unaligned_read##size);                            \
     void __tsan_write##size(void *ptr);                                    \
     void __tsan_write##size(void *ptr)                                     \
     {                                                                      \
         check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_);         \
     }                                                                      \
     EXPORT_SYMBOL(__tsan_write##size);                                     \
     void __tsan_unaligned_write##size(void *ptr)                           \
         __alias(__tsan_write##size);                                   \
     EXPORT_SYMBOL(__tsan_unaligned_write##size);                           \
     void __tsan_read_write##size(void *ptr);                               \
     void __tsan_read_write##size(void *ptr)                                \
     {                                                                      \
         check_access(ptr, size,                                        \
                  KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE,       \
                  _RET_IP_);                                        \
     }                                                                      \
     EXPORT_SYMBOL(__tsan_read_write##size);                                \
     void __tsan_unaligned_read_write##size(void *ptr)                      \
         __alias(__tsan_read_write##size);                              \
     EXPORT_SYMBOL(__tsan_unaligned_read_write##size)
 
 DEFINE_TSAN_READ_WRITE(1);
 DEFINE_TSAN_READ_WRITE(2);
 DEFINE_TSAN_READ_WRITE(4);
 DEFINE_TSAN_READ_WRITE(8);
 DEFINE_TSAN_READ_WRITE(16);
 
 void __tsan_read_range(void *ptr, size_t size);
 void __tsan_read_range(void *ptr, size_t size)
 {
     check_access(ptr, size, 0, _RET_IP_);
 }
 EXPORT_SYMBOL(__tsan_read_range);
 
 void __tsan_write_range(void *ptr, size_t size);
 void __tsan_write_range(void *ptr, size_t size)
 {
     check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_);
 }
 EXPORT_SYMBOL(__tsan_write_range);
 
 /*
  * Use of explicit volatile is generally disallowed [1], however, volatile is
  * still used in various concurrent context, whether in low-level
  * synchronization primitives or for legacy reasons.
  * [1] https://lwn.net/Articles/233479/
  *
  * We only consider volatile accesses atomic if they are aligned and would pass
  * the size-check of compiletime_assert_rwonce_type().
  */
 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size)                                  \
     void __tsan_volatile_read##size(void *ptr);                            \
     void __tsan_volatile_read##size(void *ptr)                             \
     {                                                                      \
         const bool is_atomic = size <= sizeof(long long) &&            \
                        IS_ALIGNED((unsigned long)ptr, size);   \
         if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
             return;                                                \
         check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0,   \
                  _RET_IP_);                                        \
     }                                                                      \
     EXPORT_SYMBOL(__tsan_volatile_read##size);                             \
     void __tsan_unaligned_volatile_read##size(void *ptr)                   \
         __alias(__tsan_volatile_read##size);                           \
     EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size);                   \
     void __tsan_volatile_write##size(void *ptr);                           \
     void __tsan_volatile_write##size(void *ptr)                            \
     {                                                                      \
         const bool is_atomic = size <= sizeof(long long) &&            \
                        IS_ALIGNED((unsigned long)ptr, size);   \
         if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
             return;                                                \
         check_access(ptr, size,                                        \
                  KCSAN_ACCESS_WRITE |                              \
                      (is_atomic ? KCSAN_ACCESS_ATOMIC : 0),    \
                  _RET_IP_);                                        \
     }                                                                      \
     EXPORT_SYMBOL(__tsan_volatile_write##size);                            \
     void __tsan_unaligned_volatile_write##size(void *ptr)                  \
         __alias(__tsan_volatile_write##size);                          \
     EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size)
 
 DEFINE_TSAN_VOLATILE_READ_WRITE(1);
 DEFINE_TSAN_VOLATILE_READ_WRITE(2);
 DEFINE_TSAN_VOLATILE_READ_WRITE(4);
 DEFINE_TSAN_VOLATILE_READ_WRITE(8);
 DEFINE_TSAN_VOLATILE_READ_WRITE(16);
 
 /*
  * Function entry and exit are used to determine the validty of reorder_access.
  * Reordering of the access ends at the end of the function scope where the
  * access happened. This is done for two reasons:
  *
  *  1. Artificially limits the scope where missing barriers are detected.
  *     This minimizes false positives due to uninstrumented functions that
  *     contain the required barriers but were missed.
  *
  *  2. Simplifies generating the stack trace of the access.
  */
 void __tsan_func_entry(void *call_pc);
 noinline void __tsan_func_entry(void *call_pc)
 {
     if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY))
         return;
 
     add_kcsan_stack_depth(1);
 }
 EXPORT_SYMBOL(__tsan_func_entry);
 
 void __tsan_func_exit(void);
 noinline void __tsan_func_exit(void)
 {
     struct kcsan_scoped_access *reorder_access;
 
     if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY))
         return;
 
     reorder_access = get_reorder_access(get_ctx());
     if (!reorder_access)
         goto out;
 
     if (get_kcsan_stack_depth() <= reorder_access->stack_depth) {
         /*
          * Access check to catch cases where write without a barrier
          * (supposed release) was last access in function: because
          * instrumentation is inserted before the real access, a data
          * race due to the write giving up a c-s would only be caught if
          * we do the conflicting access after.
          */
         check_access(reorder_access->ptr, reorder_access->size,
                  reorder_access->type, reorder_access->ip);
         reorder_access->size = 0;
         reorder_access->stack_depth = INT_MIN;
     }
 out:
     add_kcsan_stack_depth(-1);
 }
 EXPORT_SYMBOL(__tsan_func_exit);
 
 void __tsan_init(void);
 void __tsan_init(void)
 {
 }
 EXPORT_SYMBOL(__tsan_init);
 
 /*
  * Instrumentation for atomic builtins (__atomic_*, __sync_*).
  *
  * Normal kernel code _should not_ be using them directly, but some
  * architectures may implement some or all atomics using the compilers'
  * builtins.
  *
  * Note: If an architecture decides to fully implement atomics using the
  * builtins, because they are implicitly instrumented by KCSAN (and KASAN,
  * etc.), implementing the ARCH_ATOMIC interface (to get instrumentation via
  * atomic-instrumented) is no longer necessary.
  *
  * TSAN instrumentation replaces atomic accesses with calls to any of the below
  * functions, whose job is to also execute the operation itself.
  */
 
 static __always_inline void kcsan_atomic_builtin_memorder(int memorder)
 {
     if (memorder == __ATOMIC_RELEASE ||
         memorder == __ATOMIC_SEQ_CST ||
         memorder == __ATOMIC_ACQ_REL)
         __kcsan_release();
 }
 
 #define DEFINE_TSAN_ATOMIC_LOAD_STORE(bits)                                                        \
     u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder);                      \
     u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder)                       \
     {                                                                                          \
         kcsan_atomic_builtin_memorder(memorder);                                           \
         if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
             check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC, _RET_IP_);    \
         }                                                                                  \
         return __atomic_load_n(ptr, memorder);                                             \
     }                                                                                          \
     EXPORT_SYMBOL(__tsan_atomic##bits##_load);                                                 \
     void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder);                   \
     void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder)                    \
     {                                                                                          \
         kcsan_atomic_builtin_memorder(memorder);                                           \
         if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
             check_access(ptr, bits / BITS_PER_BYTE,                                    \
                      KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC, _RET_IP_);          \
         }                                                                                  \
         __atomic_store_n(ptr, v, memorder);                                                \
     }                                                                                          \
     EXPORT_SYMBOL(__tsan_atomic##bits##_store)
 
 #define DEFINE_TSAN_ATOMIC_RMW(op, bits, suffix)                                                   \
     u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder);                 \
     u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder)                  \
     {                                                                                          \
         kcsan_atomic_builtin_memorder(memorder);                                           \
         if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
             check_access(ptr, bits / BITS_PER_BYTE,                                    \
                      KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
                          KCSAN_ACCESS_ATOMIC, _RET_IP_);                       \
         }                                                                                  \
         return __atomic_##op##suffix(ptr, v, memorder);                                    \
     }                                                                                          \
     EXPORT_SYMBOL(__tsan_atomic##bits##_##op)
 
 /*
  * Note: CAS operations are always classified as write, even in case they
  * fail. We cannot perform check_access() after a write, as it might lead to
  * false positives, in cases such as:
  *
  *  T0: __atomic_compare_exchange_n(&p->flag, &old, 1, ...)
  *
  *  T1: if (__atomic_load_n(&p->flag, ...)) {
  *      modify *p;
  *      p->flag = 0;
  *      }
  *
  * The only downside is that, if there are 3 threads, with one CAS that
  * succeeds, another CAS that fails, and an unmarked racing operation, we may
  * point at the wrong CAS as the source of the race. However, if we assume that
  * all CAS can succeed in some other execution, the data race is still valid.
  */
 #define DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strength, weak)                                           \
     int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
                                   u##bits val, int mo, int fail_mo);   \
     int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
                                   u##bits val, int mo, int fail_mo)    \
     {                                                                                          \
         kcsan_atomic_builtin_memorder(mo);                                                 \
         if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
             check_access(ptr, bits / BITS_PER_BYTE,                                    \
                      KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
                          KCSAN_ACCESS_ATOMIC, _RET_IP_);                       \
         }                                                                                  \
         return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo);              \
     }                                                                                          \
     EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength)
 
 #define DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits)                                                       \
     u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
                                int mo, int fail_mo);                   \
     u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
                                int mo, int fail_mo)                    \
     {                                                                                          \
         kcsan_atomic_builtin_memorder(mo);                                                 \
         if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
             check_access(ptr, bits / BITS_PER_BYTE,                                    \
                      KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
                          KCSAN_ACCESS_ATOMIC, _RET_IP_);                       \
         }                                                                                  \
         __atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo);                       \
         return exp;                                                                        \
     }                                                                                          \
     EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_val)
 
 #define DEFINE_TSAN_ATOMIC_OPS(bits)                                                               \
     DEFINE_TSAN_ATOMIC_LOAD_STORE(bits);                                                       \
     DEFINE_TSAN_ATOMIC_RMW(exchange, bits, _n);                                                \
     DEFINE_TSAN_ATOMIC_RMW(fetch_add, bits, );                                                 \
     DEFINE_TSAN_ATOMIC_RMW(fetch_sub, bits, );                                                 \
     DEFINE_TSAN_ATOMIC_RMW(fetch_and, bits, );                                                 \
     DEFINE_TSAN_ATOMIC_RMW(fetch_or, bits, );                                                  \
     DEFINE_TSAN_ATOMIC_RMW(fetch_xor, bits, );                                                 \
     DEFINE_TSAN_ATOMIC_RMW(fetch_nand, bits, );                                                \
     DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strong, 0);                                               \
     DEFINE_TSAN_ATOMIC_CMPXCHG(bits, weak, 1);                                                 \
     DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits)
 
 DEFINE_TSAN_ATOMIC_OPS(8);
 DEFINE_TSAN_ATOMIC_OPS(16);
 DEFINE_TSAN_ATOMIC_OPS(32);
 DEFINE_TSAN_ATOMIC_OPS(64);
 
 void __tsan_atomic_thread_fence(int memorder);
 void __tsan_atomic_thread_fence(int memorder)
 {
     kcsan_atomic_builtin_memorder(memorder);
     __atomic_thread_fence(memorder);
 }
 EXPORT_SYMBOL(__tsan_atomic_thread_fence);
 
 /*
  * In instrumented files, we emit instrumentation for barriers by mapping the
  * kernel barriers to an __atomic_signal_fence(), which is interpreted specially
  * and otherwise has no relation to a real __atomic_signal_fence(). No known
  * kernel code uses __atomic_signal_fence().
  *
  * Since fsanitize=thread instrumentation handles __atomic_signal_fence(), which
  * are turned into calls to __tsan_atomic_signal_fence(), such instrumentation
  * can be disabled via the __no_kcsan function attribute (vs. an explicit call
  * which could not). When __no_kcsan is requested, __atomic_signal_fence()
  * generates no code.
  *
  * Note: The result of using __atomic_signal_fence() with KCSAN enabled is
  * potentially limiting the compiler's ability to reorder operations; however,
  * if barriers were instrumented with explicit calls (without LTO), the compiler
  * couldn't optimize much anyway. The result of a hypothetical architecture
  * using __atomic_signal_fence() in normal code would be KCSAN false negatives.
  */
 void __tsan_atomic_signal_fence(int memorder);
 noinline void __tsan_atomic_signal_fence(int memorder)
 {
     switch (memorder) {
     case __KCSAN_BARRIER_TO_SIGNAL_FENCE_mb:
         __kcsan_mb();
         break;
     case __KCSAN_BARRIER_TO_SIGNAL_FENCE_wmb:
         __kcsan_wmb();
         break;
     case __KCSAN_BARRIER_TO_SIGNAL_FENCE_rmb:
         __kcsan_rmb();
         break;
     case __KCSAN_BARRIER_TO_SIGNAL_FENCE_release:
         __kcsan_release();
         break;
     default:
         break;
     }
 }
 EXPORT_SYMBOL(__tsan_atomic_signal_fence);

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