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Commit 4fb6e250 authored by Tejun Heo's avatar Tejun Heo
Browse files

percpu-refcount: implement percpu_ref_tryget() 



Implement percpu_ref_tryget() which fails if the refcnt already
reached zero.  Note that this is different from the recently renamed
percpu_ref_tryget_live() which fails if the refcnt has been killed and
is draining the remaining references.  percpu_ref_tryget() succeeds on
a killed refcnt as long as its current refcnt is above zero.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarKent Overstreet <kmo@daterainc.com>
parent 2070d50e

include/linux/percpu-refcount.h

+32 −0
Original line number Original line Diff line number Diff line
@@ -117,6 +117,36 @@ static inline void percpu_ref_get(struct percpu_ref *ref) 
	rcu_read_unlock_sched();

	rcu_read_unlock_sched();

}

}





/**

 * 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.

 *

 * The caller is responsible for ensuring that @ref stays accessible.

 */

static inline bool percpu_ref_tryget(struct percpu_ref *ref)

{

	unsigned __percpu *pcpu_count;

	int ret = false;



	rcu_read_lock_sched();



	pcpu_count = ACCESS_ONCE(ref->pcpu_count);



	if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR)) {

		__this_cpu_inc(*pcpu_count);

		ret = true;

	} else {

		ret = atomic_inc_not_zero(&ref->count);

	}



	rcu_read_unlock_sched();



	return ret;

}



/**

/**

 * percpu_ref_tryget_live - try to increment a live percpu refcount

 * percpu_ref_tryget_live - try to increment a live percpu refcount

 * @ref: percpu_ref to try-get

 * @ref: percpu_ref to try-get
@@ -128,6 +158,8 @@ static inline void percpu_ref_get(struct percpu_ref *ref) 
 * will fail.  For such guarantee, percpu_ref_kill_and_confirm() should be

 * will fail.  For such guarantee, percpu_ref_kill_and_confirm() should be

 * used.  After the confirm_kill callback is invoked, it's guaranteed that

 * used.  After the confirm_kill callback is invoked, it's guaranteed that

 * no new reference will be given out by percpu_ref_tryget().

 * no new reference will be given out by percpu_ref_tryget().

 *

 * The caller is responsible for ensuring that @ref stays accessible.

 */

 */

static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)

static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)

{

{