OSCL-LXR linux-6.0.1/​include/​linux/​percpu-refcount.h	Source navigation Diff markup Identifier search General search
	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 */
 /*
  * Percpu refcounts:
  * (C) 2012 Google, Inc.
  * Author: Kent Overstreet <koverstreet@google.com>
  *
  * This implements a refcount with similar semantics to atomic_t - atomic_inc(),
  * atomic_dec_and_test() - but percpu.
  *
  * There's one important difference between percpu refs and normal atomic_t
  * refcounts; you have to keep track of your initial refcount, and then when you
  * start shutting down you call percpu_ref_kill() _before_ dropping the initial
  * refcount.
  *
  * The refcount will have a range of 0 to ((1U << 31) - 1), i.e. one bit less
  * than an atomic_t - this is because of the way shutdown works, see
  * percpu_ref_kill()/PERCPU_COUNT_BIAS.
  *
  * Before you call percpu_ref_kill(), percpu_ref_put() does not check for the
  * refcount hitting 0 - it can't, if it was in percpu mode. percpu_ref_kill()
  * puts the ref back in single atomic_t mode, collecting the per cpu refs and
  * issuing the appropriate barriers, and then marks the ref as shutting down so
  * that percpu_ref_put() will check for the ref hitting 0.  After it returns,
  * it's safe to drop the initial ref.
  *
  * USAGE:
  *
  * See fs/aio.c for some example usage; it's used there for struct kioctx, which
  * is created when userspaces calls io_setup(), and destroyed when userspace
  * calls io_destroy() or the process exits.
  *
  * In the aio code, kill_ioctx() is called when we wish to destroy a kioctx; it
  * removes the kioctx from the proccess's table of kioctxs and kills percpu_ref.
  * After that, there can't be any new users of the kioctx (from lookup_ioctx())
  * and it's then safe to drop the initial ref with percpu_ref_put().
  *
  * Note that the free path, free_ioctx(), needs to go through explicit call_rcu()
  * to synchronize with RCU protected lookup_ioctx().  percpu_ref operations don't
  * imply RCU grace periods of any kind and if a user wants to combine percpu_ref
  * with RCU protection, it must be done explicitly.
  *
  * Code that does a two stage shutdown like this often needs some kind of
  * explicit synchronization to ensure the initial refcount can only be dropped
  * once - percpu_ref_kill() does this for you, it returns true once and false if
  * someone else already called it. The aio code uses it this way, but it's not
  * necessary if the code has some other mechanism to synchronize teardown.
  * around.
  */
 
 #ifndef _LINUX_PERCPU_REFCOUNT_H
 #define _LINUX_PERCPU_REFCOUNT_H
 
 #include <linux/atomic.h>
 #include <linux/percpu.h>
 #include <linux/rcupdate.h>
 #include <linux/types.h>
 #include <linux/gfp.h>
 
 struct percpu_ref;
 typedef void (percpu_ref_func_t)(struct percpu_ref *);
 
 /* flags set in the lower bits of percpu_ref->percpu_count_ptr */
 enum {
     __PERCPU_REF_ATOMIC = 1LU << 0, /* operating in atomic mode */
     __PERCPU_REF_DEAD   = 1LU << 1, /* (being) killed */
     __PERCPU_REF_ATOMIC_DEAD = __PERCPU_REF_ATOMIC | __PERCPU_REF_DEAD,
 
     __PERCPU_REF_FLAG_BITS  = 2,
 };
 
 /* @flags for percpu_ref_init() */
 enum {
     /*
      * Start w/ ref == 1 in atomic mode.  Can be switched to percpu
      * operation using percpu_ref_switch_to_percpu().  If initialized
      * with this flag, the ref will stay in atomic mode until
      * percpu_ref_switch_to_percpu() is invoked on it.
      * Implies ALLOW_REINIT.
      */
     PERCPU_REF_INIT_ATOMIC  = 1 << 0,
 
     /*
      * Start dead w/ ref == 0 in atomic mode.  Must be revived with
      * percpu_ref_reinit() before used.  Implies INIT_ATOMIC and
      * ALLOW_REINIT.
      */
     PERCPU_REF_INIT_DEAD    = 1 << 1,
 
     /*
      * Allow switching from atomic mode to percpu mode.
      */
     PERCPU_REF_ALLOW_REINIT = 1 << 2,
 };
 
 struct percpu_ref_data {
     atomic_long_t       count;
     percpu_ref_func_t   *release;
     percpu_ref_func_t   *confirm_switch;
     bool            force_atomic:1;
     bool            allow_reinit:1;
     struct rcu_head     rcu;
     struct percpu_ref   *ref;
 };
 
 struct percpu_ref {
     /*
      * The low bit of the pointer indicates whether the ref is in percpu
      * mode; if set, then get/put will manipulate the atomic_t.
      */
     unsigned long       percpu_count_ptr;
 
     /*
      * 'percpu_ref' is often embedded into user structure, and only
      * 'percpu_count_ptr' is required in fast path, move other fields
      * into 'percpu_ref_data', so we can reduce memory footprint in
      * fast path.
      */
     struct percpu_ref_data  *data;
 };
 
 int __must_check percpu_ref_init(struct percpu_ref *ref,
                  percpu_ref_func_t *release, unsigned int flags,
                  gfp_t gfp);
 void percpu_ref_exit(struct percpu_ref *ref);
 void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
                  percpu_ref_func_t *confirm_switch);
 void percpu_ref_switch_to_atomic_sync(struct percpu_ref *ref);
 void percpu_ref_switch_to_percpu(struct percpu_ref *ref);
 void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
                  percpu_ref_func_t *confirm_kill);
 void percpu_ref_resurrect(struct percpu_ref *ref);
 void percpu_ref_reinit(struct percpu_ref *ref);
 bool percpu_ref_is_zero(struct percpu_ref *ref);
 
 /**
  * percpu_ref_kill - drop the initial ref
  * @ref: percpu_ref to kill
  *
  * Must be used to drop the initial ref on a percpu refcount; must be called
  * precisely once before shutdown.
  *
  * Switches @ref into atomic mode before gathering up the percpu counters
  * and dropping the initial ref.
  *
  * There are no implied RCU grace periods between kill and release.
  */
 static inline void percpu_ref_kill(struct percpu_ref *ref)
 {
     percpu_ref_kill_and_confirm(ref, NULL);
 }
 
 /*
  * Internal helper.  Don't use outside percpu-refcount proper.  The
  * function doesn't return the pointer and let the caller test it for NULL
  * because doing so forces the compiler to generate two conditional
  * branches as it can't assume that @ref->percpu_count is not NULL.
  */
 static inline bool __ref_is_percpu(struct percpu_ref *ref,
                       unsigned long __percpu **percpu_countp)
 {
     unsigned long percpu_ptr;
 
     /*
      * The value of @ref->percpu_count_ptr is tested for
      * !__PERCPU_REF_ATOMIC, which may be set asynchronously, and then
      * used as a pointer.  If the compiler generates a separate fetch
      * when using it as a pointer, __PERCPU_REF_ATOMIC may be set in
      * between contaminating the pointer value, meaning that
      * READ_ONCE() is required when fetching it.
      *
      * The dependency ordering from the READ_ONCE() pairs
      * with smp_store_release() in __percpu_ref_switch_to_percpu().
      */
     percpu_ptr = READ_ONCE(ref->percpu_count_ptr);
 
     /*
      * Theoretically, the following could test just ATOMIC; however,
      * then we'd have to mask off DEAD separately as DEAD may be
      * visible without ATOMIC if we race with percpu_ref_kill().  DEAD
      * implies ATOMIC anyway.  Test them together.
      */
     if (unlikely(percpu_ptr & __PERCPU_REF_ATOMIC_DEAD))
         return false;
 
     *percpu_countp = (unsigned long __percpu *)percpu_ptr;
     return true;
 }
 
 /**
  * percpu_ref_get_many - increment a percpu refcount
  * @ref: percpu_ref to get
  * @nr: number of references to get
  *
  * Analogous to atomic_long_add().
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
 static inline void percpu_ref_get_many(struct percpu_ref *ref, unsigned long nr)
 {
     unsigned long __percpu *percpu_count;
 
     rcu_read_lock();
 
     if (__ref_is_percpu(ref, &percpu_count))
         this_cpu_add(*percpu_count, nr);
     else
         atomic_long_add(nr, &ref->data->count);
 
     rcu_read_unlock();
 }
 
 /**
  * percpu_ref_get - increment a percpu refcount
  * @ref: percpu_ref to get
  *
  * Analogous to atomic_long_inc().
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
 static inline void percpu_ref_get(struct percpu_ref *ref)
 {
     percpu_ref_get_many(ref, 1);
 }
 
 /**
  * percpu_ref_tryget_many - try to increment a percpu refcount
  * @ref: percpu_ref to try-get
  * @nr: number of references to get
  *
  * Increment a percpu refcount  by @nr unless its count already reached zero.
  * Returns %true on success; %false on failure.
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
 static inline bool percpu_ref_tryget_many(struct percpu_ref *ref,
                       unsigned long nr)
 {
     unsigned long __percpu *percpu_count;
     bool ret;
 
     rcu_read_lock();
 
     if (__ref_is_percpu(ref, &percpu_count)) {
         this_cpu_add(*percpu_count, nr);
         ret = true;
     } else {
         ret = atomic_long_add_unless(&ref->data->count, nr, 0);
     }
 
     rcu_read_unlock();
 
     return ret;
 }
 
 /**
  * percpu_ref_tryget - try to increment a percpu refcount
  * @ref: percpu_ref to try-get
  *
  * Increment a percpu refcount unless its count already reached zero.
  * Returns %true on success; %false on failure.
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
 static inline bool percpu_ref_tryget(struct percpu_ref *ref)
 {
     return percpu_ref_tryget_many(ref, 1);
 }
 
 /**
  * percpu_ref_tryget_live_rcu - same as percpu_ref_tryget_live() but the
  * caller is responsible for taking RCU.
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
 static inline bool percpu_ref_tryget_live_rcu(struct percpu_ref *ref)
 {
     unsigned long __percpu *percpu_count;
     bool ret = false;
 
     WARN_ON_ONCE(!rcu_read_lock_held());
 
     if (likely(__ref_is_percpu(ref, &percpu_count))) {
         this_cpu_inc(*percpu_count);
         ret = true;
     } else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) {
         ret = atomic_long_inc_not_zero(&ref->data->count);
     }
     return ret;
 }
 
 /**
  * percpu_ref_tryget_live - try to increment a live percpu refcount
  * @ref: percpu_ref to try-get
  *
  * Increment a percpu refcount unless it has already been killed.  Returns
  * %true on success; %false on failure.
  *
  * Completion of percpu_ref_kill() in itself doesn't guarantee that this
  * function will fail.  For such guarantee, percpu_ref_kill_and_confirm()
  * should be used.  After the confirm_kill callback is invoked, it's
  * guaranteed that no new reference will be given out by
  * percpu_ref_tryget_live().
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
 static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
 {
     bool ret = false;
 
     rcu_read_lock();
     ret = percpu_ref_tryget_live_rcu(ref);
     rcu_read_unlock();
     return ret;
 }
 
 /**
  * percpu_ref_put_many - decrement a percpu refcount
  * @ref: percpu_ref to put
  * @nr: number of references to put
  *
  * Decrement the refcount, and if 0, call the release function (which was passed
  * to percpu_ref_init())
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
 static inline void percpu_ref_put_many(struct percpu_ref *ref, unsigned long nr)
 {
     unsigned long __percpu *percpu_count;
 
     rcu_read_lock();
 
     if (__ref_is_percpu(ref, &percpu_count))
         this_cpu_sub(*percpu_count, nr);
     else if (unlikely(atomic_long_sub_and_test(nr, &ref->data->count)))
         ref->data->release(ref);
 
     rcu_read_unlock();
 }
 
 /**
  * percpu_ref_put - decrement a percpu refcount
  * @ref: percpu_ref to put
  *
  * Decrement the refcount, and if 0, call the release function (which was passed
  * to percpu_ref_init())
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
 static inline void percpu_ref_put(struct percpu_ref *ref)
 {
     percpu_ref_put_many(ref, 1);
 }
 
 /**
  * percpu_ref_is_dying - test whether a percpu refcount is dying or dead
  * @ref: percpu_ref to test
  *
  * Returns %true if @ref is dying or dead.
  *
  * This function is safe to call as long as @ref is between init and exit
  * and the caller is responsible for synchronizing against state changes.
  */
 static inline bool percpu_ref_is_dying(struct percpu_ref *ref)
 {
     return ref->percpu_count_ptr & __PERCPU_REF_DEAD;
 }
 
 #endif

This page was automatically generated by the 2.1.0 LXR engine. The LXR team