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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 /lib/percpu-refcount.c | |
parent | 9a1049da9bd2cd83fe11d46433e603c193aa9c71 (diff) | |
download | linux-stable-2d7227828e1475c7b272e55bd70c4cec8eea219a.tar.gz linux-stable-2d7227828e1475c7b272e55bd70c4cec8eea219a.tar.bz2 linux-stable-2d7227828e1475c7b272e55bd70c4cec8eea219a.zip |
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 'lib/percpu-refcount.c')
-rw-r--r-- | lib/percpu-refcount.c | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index ac4299120087..fe5a3342e960 100644 --- a/lib/percpu-refcount.c +++ b/lib/percpu-refcount.c @@ -61,6 +61,41 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release) EXPORT_SYMBOL_GPL(percpu_ref_init); /** + * percpu_ref_reinit - re-initialize a percpu refcount + * @ref: perpcu_ref to re-initialize + * + * Re-initialize @ref so that it's in the same state as when it finished + * percpu_ref_init(). @ref must have been initialized successfully, killed + * and reached 0 but not exited. + * + * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while + * this function is in progress. + */ +void percpu_ref_reinit(struct percpu_ref *ref) +{ + unsigned __percpu *pcpu_count = pcpu_count_ptr(ref); + int cpu; + + BUG_ON(!pcpu_count); + WARN_ON(!percpu_ref_is_zero(ref)); + + atomic_set(&ref->count, 1 + PCPU_COUNT_BIAS); + + /* + * Restore per-cpu operation. smp_store_release() is paired with + * smp_read_barrier_depends() in __pcpu_ref_alive() and guarantees + * that the zeroing is visible to all percpu accesses which can see + * the following PCPU_REF_DEAD clearing. + */ + for_each_possible_cpu(cpu) + *per_cpu_ptr(pcpu_count, cpu) = 0; + + smp_store_release(&ref->pcpu_count_ptr, + ref->pcpu_count_ptr & ~PCPU_REF_DEAD); +} +EXPORT_SYMBOL_GPL(percpu_ref_reinit); + +/** * percpu_ref_exit - undo percpu_ref_init() * @ref: percpu_ref to exit * |