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 <[email protected]> Cc: Kent Overstreet <[email protected]> --- include/linux/percpu-refcount.h | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -118,6 +118,36 @@ static inline void percpu_ref_get(struct } /** + * 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 * 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) { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
