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author | Tejun Heo <tj@kernel.org> | 2014-06-28 08:10:14 -0400 |
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committer | Tejun Heo <tj@kernel.org> | 2014-06-28 08:10:14 -0400 |
commit | 2d7227828e1475c7b272e55bd70c4cec8eea219a (patch) | |
tree | 068171c424acc2390b1e6ecf514182c82cc5811d /include | |
parent | 9a1049da9bd2cd83fe11d46433e603c193aa9c71 (diff) | |
download | linux-2d7227828e1475c7b272e55bd70c4cec8eea219a.tar.bz2 |
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 <tj@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/percpu-refcount.h | 19 |
1 files changed, 19 insertions, 0 deletions
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 |