From 2d7227828e1475c7b272e55bd70c4cec8eea219a Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sat, 28 Jun 2014 08:10:14 -0400 Subject: percpu-refcount: implement percpu_ref_reinit() and percpu_ref_is_zero() Now that explicit invocation of percpu_ref_exit() is necessary to free the percpu counter, we can implement percpu_ref_reinit() which reinitializes a released percpu_ref. This can be used implement scalable gating switch which can be drained and then re-opened without worrying about memory allocation failures. percpu_ref_is_zero() is added to be used in a sanity check in percpu_ref_exit(). As this function will be useful for other purposes too, make it a public interface. v2: Use smp_read_barrier_depends() instead of smp_load_acquire(). We only need data dep barrier and smp_load_acquire() is stronger and heavier on some archs. Spotted by Lai Jiangshan. Signed-off-by: Tejun Heo Cc: Kent Overstreet Cc: Christoph Lameter Cc: Lai Jiangshan --- include/linux/percpu-refcount.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'include') diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h index 0ddd2839ca84..3dfbf237cd8f 100644 --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -67,6 +67,7 @@ struct percpu_ref { int __must_check percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release); +void percpu_ref_reinit(struct percpu_ref *ref); void percpu_ref_exit(struct percpu_ref *ref); void percpu_ref_kill_and_confirm(struct percpu_ref *ref, percpu_ref_func_t *confirm_kill); @@ -99,6 +100,9 @@ static inline bool __pcpu_ref_alive(struct percpu_ref *ref, { unsigned long pcpu_ptr = ACCESS_ONCE(ref->pcpu_count_ptr); + /* paired with smp_store_release() in percpu_ref_reinit() */ + smp_read_barrier_depends(); + if (unlikely(pcpu_ptr & PCPU_REF_DEAD)) return false; @@ -206,4 +210,19 @@ static inline void percpu_ref_put(struct percpu_ref *ref) rcu_read_unlock_sched(); } +/** + * percpu_ref_is_zero - test whether a percpu refcount reached zero + * @ref: percpu_ref to test + * + * Returns %true if @ref reached zero. + */ +static inline bool percpu_ref_is_zero(struct percpu_ref *ref) +{ + unsigned __percpu *pcpu_count; + + if (__pcpu_ref_alive(ref, &pcpu_count)) + return false; + return !atomic_read(&ref->count); +} + #endif -- cgit v1.2.3