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Merge branch 'for-3.20' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu

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Pull percpu changes from Tejun Heo:
 "Nothing too interesting.  One cleanup patch and another to add a
  trivial state check function"

* 'for-3.20' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu:
  percpu_ref: implement percpu_ref_is_dying()
  percpu_ref: remove unnecessary ACCESS_ONCE() in percpu_ref_tryget_live()
This commit is contained in:
Linus Torvalds 2015-02-09 18:55:45 -08:00
commit c2189e3a3d
1 changed files with 31 additions and 3 deletions
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34
include/linux/percpu-refcount.h
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@ -128,8 +128,22 @@ static inline void percpu_ref_kill(struct percpu_ref *ref)
static inline bool __ref_is_percpu(struct percpu_ref *ref,
unsigned long __percpu **percpu_countp)
{
/* paired with smp_store_release() in percpu_ref_reinit() */
unsigned long percpu_ptr = lockless_dereference(ref->percpu_count_ptr);
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
* ACCESS_ONCE() is required when fetching it.
*
* Also, we need a data dependency barrier to be paired with
* smp_store_release() in __percpu_ref_switch_to_percpu().
*
* Use lockless deref which contains both.
*/
percpu_ptr = lockless_dereference(ref->percpu_count_ptr);
/*
* Theoretically, the following could test just ATOMIC; however,
@ -233,7 +247,7 @@ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
if (__ref_is_percpu(ref, &percpu_count)) {
this_cpu_inc(*percpu_count);
ret = true;
} else if (!(ACCESS_ONCE(ref->percpu_count_ptr) & __PERCPU_REF_DEAD)) {
} else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) {
ret = atomic_long_inc_not_zero(&ref->count);
}
@ -280,6 +294,20 @@ 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;
}
/**
* percpu_ref_is_zero - test whether a percpu refcount reached zero
* @ref: percpu_ref to test