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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 #define pr_fmt(fmt) "%s: " fmt, __func__
 
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
 #include <linux/slab.h>
 #include <linux/mm.h>
 #include <linux/percpu-refcount.h>
 
 /*
  * Initially, a percpu refcount is just a set of percpu counters. Initially, we
  * don't try to detect the ref hitting 0 - which means that get/put can just
  * increment or decrement the local counter. Note that the counter on a
  * particular cpu can (and will) wrap - this is fine, when we go to shutdown the
  * percpu counters will all sum to the correct value
  *
  * (More precisely: because modular arithmetic is commutative the sum of all the
  * percpu_count vars will be equal to what it would have been if all the gets
  * and puts were done to a single integer, even if some of the percpu integers
  * overflow or underflow).
  *
  * The real trick to implementing percpu refcounts is shutdown. We can't detect
  * the ref hitting 0 on every put - this would require global synchronization
  * and defeat the whole purpose of using percpu refs.
  *
  * What we do is require the user to keep track of the initial refcount; we know
  * the ref can't hit 0 before the user drops the initial ref, so as long as we
  * convert to non percpu mode before the initial ref is dropped everything
  * works.
  *
  * Converting to non percpu mode is done with some RCUish stuff in
  * percpu_ref_kill. Additionally, we need a bias value so that the
  * atomic_long_t can't hit 0 before we've added up all the percpu refs.
  */
 
 #define PERCPU_COUNT_BIAS   (1LU << (BITS_PER_LONG - 1))
 
 static DEFINE_SPINLOCK(percpu_ref_switch_lock);
 static DECLARE_WAIT_QUEUE_HEAD(percpu_ref_switch_waitq);
 
 static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
 {
     return (unsigned long __percpu *)
         (ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD);
 }
 
 /**
  * percpu_ref_init - initialize a percpu refcount
  * @ref: percpu_ref to initialize
  * @release: function which will be called when refcount hits 0
  * @flags: PERCPU_REF_INIT_* flags
  * @gfp: allocation mask to use
  *
  * Initializes @ref.  @ref starts out in percpu mode with a refcount of 1 unless
  * @flags contains PERCPU_REF_INIT_ATOMIC or PERCPU_REF_INIT_DEAD.  These flags
  * change the start state to atomic with the latter setting the initial refcount
  * to 0.  See the definitions of PERCPU_REF_INIT_* flags for flag behaviors.
  *
  * Note that @release must not sleep - it may potentially be called from RCU
  * callback context by percpu_ref_kill().
  */
 int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
             unsigned int flags, gfp_t gfp)
 {
     size_t align = max_t(size_t, 1 << __PERCPU_REF_FLAG_BITS,
                  __alignof__(unsigned long));
     unsigned long start_count = 0;
     struct percpu_ref_data *data;
 
     ref->percpu_count_ptr = (unsigned long)
         __alloc_percpu_gfp(sizeof(unsigned long), align, gfp);
     if (!ref->percpu_count_ptr)
         return -ENOMEM;
 
     data = kzalloc(sizeof(*ref->data), gfp);
     if (!data) {
         free_percpu((void __percpu *)ref->percpu_count_ptr);
         ref->percpu_count_ptr = 0;
         return -ENOMEM;
     }
 
     data->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;
     data->allow_reinit = flags & PERCPU_REF_ALLOW_REINIT;
 
     if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD)) {
         ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
         data->allow_reinit = true;
     } else {
         start_count += PERCPU_COUNT_BIAS;
     }
 
     if (flags & PERCPU_REF_INIT_DEAD)
         ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
     else
         start_count++;
 
     atomic_long_set(&data->count, start_count);
 
     data->release = release;
     data->confirm_switch = NULL;
     data->ref = ref;
     ref->data = data;
     return 0;
 }
 EXPORT_SYMBOL_GPL(percpu_ref_init);
 
 static void __percpu_ref_exit(struct percpu_ref *ref)
 {
     unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
 
     if (percpu_count) {
         /* non-NULL confirm_switch indicates switching in progress */
         WARN_ON_ONCE(ref->data && ref->data->confirm_switch);
         free_percpu(percpu_count);
         ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;
     }
 }
 
 /**
  * percpu_ref_exit - undo percpu_ref_init()
  * @ref: percpu_ref to exit
  *
  * This function exits @ref.  The caller is responsible for ensuring that
  * @ref is no longer in active use.  The usual places to invoke this
  * function from are the @ref->release() callback or in init failure path
  * where percpu_ref_init() succeeded but other parts of the initialization
  * of the embedding object failed.
  */
 void percpu_ref_exit(struct percpu_ref *ref)
 {
     struct percpu_ref_data *data = ref->data;
     unsigned long flags;
 
     __percpu_ref_exit(ref);
 
     if (!data)
         return;
 
     spin_lock_irqsave(&percpu_ref_switch_lock, flags);
     ref->percpu_count_ptr |= atomic_long_read(&ref->data->count) <<
         __PERCPU_REF_FLAG_BITS;
     ref->data = NULL;
     spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
 
     kfree(data);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_exit);
 
 static void percpu_ref_call_confirm_rcu(struct rcu_head *rcu)
 {
     struct percpu_ref_data *data = container_of(rcu,
             struct percpu_ref_data, rcu);
     struct percpu_ref *ref = data->ref;
 
     data->confirm_switch(ref);
     data->confirm_switch = NULL;
     wake_up_all(&percpu_ref_switch_waitq);
 
     if (!data->allow_reinit)
         __percpu_ref_exit(ref);
 
     /* drop ref from percpu_ref_switch_to_atomic() */
     percpu_ref_put(ref);
 }
 
 static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
 {
     struct percpu_ref_data *data = container_of(rcu,
             struct percpu_ref_data, rcu);
     struct percpu_ref *ref = data->ref;
     unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
     static atomic_t underflows;
     unsigned long count = 0;
     int cpu;
 
     for_each_possible_cpu(cpu)
         count += *per_cpu_ptr(percpu_count, cpu);
 
     pr_debug("global %lu percpu %lu\n",
          atomic_long_read(&data->count), count);
 
     /*
      * It's crucial that we sum the percpu counters _before_ adding the sum
      * to &ref->count; since gets could be happening on one cpu while puts
      * happen on another, adding a single cpu's count could cause
      * @ref->count to hit 0 before we've got a consistent value - but the
      * sum of all the counts will be consistent and correct.
      *
      * Subtracting the bias value then has to happen _after_ adding count to
      * &ref->count; we need the bias value to prevent &ref->count from
      * reaching 0 before we add the percpu counts. But doing it at the same
      * time is equivalent and saves us atomic operations:
      */
     atomic_long_add((long)count - PERCPU_COUNT_BIAS, &data->count);
 
     if (WARN_ONCE(atomic_long_read(&data->count) <= 0,
               "percpu ref (%ps) <= 0 (%ld) after switching to atomic",
               data->release, atomic_long_read(&data->count)) &&
         atomic_inc_return(&underflows) < 4) {
         pr_err("%s(): percpu_ref underflow", __func__);
         mem_dump_obj(data);
     }
 
     /* @ref is viewed as dead on all CPUs, send out switch confirmation */
     percpu_ref_call_confirm_rcu(rcu);
 }
 
 static void percpu_ref_noop_confirm_switch(struct percpu_ref *ref)
 {
 }
 
 static void __percpu_ref_switch_to_atomic(struct percpu_ref *ref,
                       percpu_ref_func_t *confirm_switch)
 {
     if (ref->percpu_count_ptr & __PERCPU_REF_ATOMIC) {
         if (confirm_switch)
             confirm_switch(ref);
         return;
     }
 
     /* switching from percpu to atomic */
     ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
 
     /*
      * Non-NULL ->confirm_switch is used to indicate that switching is
      * in progress.  Use noop one if unspecified.
      */
     ref->data->confirm_switch = confirm_switch ?:
         percpu_ref_noop_confirm_switch;
 
     percpu_ref_get(ref);    /* put after confirmation */
     call_rcu(&ref->data->rcu, percpu_ref_switch_to_atomic_rcu);
 }
 
 static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
 {
     unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
     int cpu;
 
     BUG_ON(!percpu_count);
 
     if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC))
         return;
 
     if (WARN_ON_ONCE(!ref->data->allow_reinit))
         return;
 
     atomic_long_add(PERCPU_COUNT_BIAS, &ref->data->count);
 
     /*
      * Restore per-cpu operation.  smp_store_release() is paired
      * with READ_ONCE() in __ref_is_percpu() and guarantees that the
      * zeroing is visible to all percpu accesses which can see the
      * following __PERCPU_REF_ATOMIC clearing.
      */
     for_each_possible_cpu(cpu)
         *per_cpu_ptr(percpu_count, cpu) = 0;
 
     smp_store_release(&ref->percpu_count_ptr,
               ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
 }
 
 static void __percpu_ref_switch_mode(struct percpu_ref *ref,
                      percpu_ref_func_t *confirm_switch)
 {
     struct percpu_ref_data *data = ref->data;
 
     lockdep_assert_held(&percpu_ref_switch_lock);
 
     /*
      * If the previous ATOMIC switching hasn't finished yet, wait for
      * its completion.  If the caller ensures that ATOMIC switching
      * isn't in progress, this function can be called from any context.
      */
     wait_event_lock_irq(percpu_ref_switch_waitq, !data->confirm_switch,
                 percpu_ref_switch_lock);
 
     if (data->force_atomic || percpu_ref_is_dying(ref))
         __percpu_ref_switch_to_atomic(ref, confirm_switch);
     else
         __percpu_ref_switch_to_percpu(ref);
 }
 
 /**
  * percpu_ref_switch_to_atomic - switch a percpu_ref to atomic mode
  * @ref: percpu_ref to switch to atomic mode
  * @confirm_switch: optional confirmation callback
  *
  * There's no reason to use this function for the usual reference counting.
  * Use percpu_ref_kill[_and_confirm]().
  *
  * Schedule switching of @ref to atomic mode.  All its percpu counts will
  * be collected to the main atomic counter.  On completion, when all CPUs
  * are guaraneed to be in atomic mode, @confirm_switch, which may not
  * block, is invoked.  This function may be invoked concurrently with all
  * the get/put operations and can safely be mixed with kill and reinit
  * operations.  Note that @ref will stay in atomic mode across kill/reinit
  * cycles until percpu_ref_switch_to_percpu() is called.
  *
  * This function may block if @ref is in the process of switching to atomic
  * mode.  If the caller ensures that @ref is not in the process of
  * switching to atomic mode, this function can be called from any context.
  */
 void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
                  percpu_ref_func_t *confirm_switch)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&percpu_ref_switch_lock, flags);
 
     ref->data->force_atomic = true;
     __percpu_ref_switch_mode(ref, confirm_switch);
 
     spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_switch_to_atomic);
 
 /**
  * percpu_ref_switch_to_atomic_sync - switch a percpu_ref to atomic mode
  * @ref: percpu_ref to switch to atomic mode
  *
  * Schedule switching the ref to atomic mode, and wait for the
  * switch to complete.  Caller must ensure that no other thread
  * will switch back to percpu mode.
  */
 void percpu_ref_switch_to_atomic_sync(struct percpu_ref *ref)
 {
     percpu_ref_switch_to_atomic(ref, NULL);
     wait_event(percpu_ref_switch_waitq, !ref->data->confirm_switch);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_switch_to_atomic_sync);
 
 /**
  * percpu_ref_switch_to_percpu - switch a percpu_ref to percpu mode
  * @ref: percpu_ref to switch to percpu mode
  *
  * There's no reason to use this function for the usual reference counting.
  * To re-use an expired ref, use percpu_ref_reinit().
  *
  * Switch @ref to percpu mode.  This function may be invoked concurrently
  * with all the get/put operations and can safely be mixed with kill and
  * reinit operations.  This function reverses the sticky atomic state set
  * by PERCPU_REF_INIT_ATOMIC or percpu_ref_switch_to_atomic().  If @ref is
  * dying or dead, the actual switching takes place on the following
  * percpu_ref_reinit().
  *
  * This function may block if @ref is in the process of switching to atomic
  * mode.  If the caller ensures that @ref is not in the process of
  * switching to atomic mode, this function can be called from any context.
  */
 void percpu_ref_switch_to_percpu(struct percpu_ref *ref)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&percpu_ref_switch_lock, flags);
 
     ref->data->force_atomic = false;
     __percpu_ref_switch_mode(ref, NULL);
 
     spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_switch_to_percpu);
 
 /**
  * percpu_ref_kill_and_confirm - drop the initial ref and schedule confirmation
  * @ref: percpu_ref to kill
  * @confirm_kill: optional confirmation callback
  *
  * Equivalent to percpu_ref_kill() but also schedules kill confirmation if
  * @confirm_kill is not NULL.  @confirm_kill, which may not block, will be
  * called after @ref is seen as dead from all CPUs at which point all
  * further invocations of percpu_ref_tryget_live() will fail.  See
  * percpu_ref_tryget_live() for details.
  *
  * This function normally doesn't block and can be called from any context
  * but it may block if @confirm_kill is specified and @ref is in the
  * process of switching to atomic mode by percpu_ref_switch_to_atomic().
  *
  * There are no implied RCU grace periods between kill and release.
  */
 void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
                  percpu_ref_func_t *confirm_kill)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&percpu_ref_switch_lock, flags);
 
     WARN_ONCE(percpu_ref_is_dying(ref),
           "%s called more than once on %ps!", __func__,
           ref->data->release);
 
     ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
     __percpu_ref_switch_mode(ref, confirm_kill);
     percpu_ref_put(ref);
 
     spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm);
 
 /**
  * percpu_ref_is_zero - test whether a percpu refcount reached zero
  * @ref: percpu_ref to test
  *
  * Returns %true if @ref reached zero.
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
 bool percpu_ref_is_zero(struct percpu_ref *ref)
 {
     unsigned long __percpu *percpu_count;
     unsigned long count, flags;
 
     if (__ref_is_percpu(ref, &percpu_count))
         return false;
 
     /* protect us from being destroyed */
     spin_lock_irqsave(&percpu_ref_switch_lock, flags);
     if (ref->data)
         count = atomic_long_read(&ref->data->count);
     else
         count = ref->percpu_count_ptr >> __PERCPU_REF_FLAG_BITS;
     spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
 
     return count == 0;
 }
 EXPORT_SYMBOL_GPL(percpu_ref_is_zero);
 
 /**
  * percpu_ref_reinit - re-initialize a percpu refcount
  * @ref: perpcu_ref to re-initialize
  *
  * Re-initialize @ref so that it's in the same state as when it finished
  * percpu_ref_init() ignoring %PERCPU_REF_INIT_DEAD.  @ref must have been
  * initialized successfully and reached 0 but not exited.
  *
  * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while
  * this function is in progress.
  */
 void percpu_ref_reinit(struct percpu_ref *ref)
 {
     WARN_ON_ONCE(!percpu_ref_is_zero(ref));
 
     percpu_ref_resurrect(ref);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_reinit);
 
 /**
  * percpu_ref_resurrect - modify a percpu refcount from dead to live
  * @ref: perpcu_ref to resurrect
  *
  * Modify @ref so that it's in the same state as before percpu_ref_kill() was
  * called. @ref must be dead but must not yet have exited.
  *
  * If @ref->release() frees @ref then the caller is responsible for
  * guaranteeing that @ref->release() does not get called while this
  * function is in progress.
  *
  * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while
  * this function is in progress.
  */
 void percpu_ref_resurrect(struct percpu_ref *ref)
 {
     unsigned long __percpu *percpu_count;
     unsigned long flags;
 
     spin_lock_irqsave(&percpu_ref_switch_lock, flags);
 
     WARN_ON_ONCE(!percpu_ref_is_dying(ref));
     WARN_ON_ONCE(__ref_is_percpu(ref, &percpu_count));
 
     ref->percpu_count_ptr &= ~__PERCPU_REF_DEAD;
     percpu_ref_get(ref);
     __percpu_ref_switch_mode(ref, NULL);
 
     spin_unlock_irqrestore(&percpu_ref_switch_lock, flags);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_resurrect);

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