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Commit c2189e3a authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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

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()
parents ed824a62 4c907baf

include/linux/percpu-refcount.h

+31 −3
Original line number Original line Diff line number Diff line
@@ -128,8 +128,22 @@ static inline void percpu_ref_kill(struct percpu_ref *ref) 
static inline bool __ref_is_percpu(struct percpu_ref *ref,

static inline bool __ref_is_percpu(struct percpu_ref *ref,

					  unsigned long __percpu **percpu_countp)

					  unsigned long __percpu **percpu_countp)

{

{

	/* paired with smp_store_release() in percpu_ref_reinit() */

	unsigned long percpu_ptr;

	unsigned long percpu_ptr = lockless_dereference(ref->percpu_count_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,

	 * 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)) {

	if (__ref_is_percpu(ref, &percpu_count)) {

		this_cpu_inc(*percpu_count);

		this_cpu_inc(*percpu_count);

		ret = true;

		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);

		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_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

 * percpu_ref_is_zero - test whether a percpu refcount reached zero

 * @ref: percpu_ref to test

 * @ref: percpu_ref to test