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percpu-refcount: add __must_check to percpu_ref_init() and don't use ACCESS_ONCE() in percpu_ref_kill_rcu() 

Two small changes.

* Unlike most init functions, percpu_ref_init() allocates memory and
  may fail.  Let's mark it with __must_check in case the caller
  forgets.

* percpu_ref_kill_rcu() is unnecessarily using ACCESS_ONCE() to
  dereference @ref->pcpu_count, which can be misleading.  The pointer
  is guaranteed to be valid and visible and can't change underneath
  the function.  Drop ACCESS_ONCE().

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2013-06-12 20:52:01 -07:00
parent ac899061a9
commit acac7883ee
2 changed files with 3 additions and 4 deletions
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3
include/linux/percpu-refcount.h
View File

@ -66,7 +66,8 @@ struct percpu_ref {
struct rcu_head rcu; struct rcu_head rcu;
}; };
int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release); int __must_check percpu_ref_init(struct percpu_ref *ref,
percpu_ref_func_t *release);
void percpu_ref_kill(struct percpu_ref *ref); void percpu_ref_kill(struct percpu_ref *ref);
#define PCPU_STATUS_BITS 2 #define PCPU_STATUS_BITS 2

4
lib/percpu-refcount.c
View File

@ -57,12 +57,10 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release)
static void percpu_ref_kill_rcu(struct rcu_head *rcu) static void percpu_ref_kill_rcu(struct rcu_head *rcu)
{ {
struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu); struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
unsigned __percpu *pcpu_count; unsigned __percpu *pcpu_count = ref->pcpu_count;
unsigned count = 0; unsigned count = 0;
int cpu; int cpu;
pcpu_count = ACCESS_ONCE(ref->pcpu_count);
/* Mask out PCPU_REF_DEAD */ /* Mask out PCPU_REF_DEAD */
pcpu_count = (unsigned __percpu *) pcpu_count = (unsigned __percpu *)
(((unsigned long) pcpu_count) & ~PCPU_STATUS_MASK); (((unsigned long) pcpu_count) & ~PCPU_STATUS_MASK);