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percpu-refcount: implement percpu_ref_tryget()

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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: Tejun Heo <tj@kernel.org>
Acked-by: Kent Overstreet <kmo@daterainc.com>
This commit is contained in:
Tejun Heo 2014-05-09 15:11:53 -04:00
commit 4fb6e25049
1 changed files with 32 additions and 0 deletions
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32
include/linux/percpu-refcount.h
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@ -117,6 +117,36 @@ static inline void percpu_ref_get(struct percpu_ref *ref)
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
* @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
* used. After the confirm_kill callback is invoked, it's guaranteed that
* 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)
{