[PATCH percpu/for-3.11 1/2] percpu-refcount: add __must_check to percpu_ref_init() and don't use ACCESS_ONCE() in percpu_ref_kill_rcu()

Tejun Heo
2013-06-13T03:52:08Z

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>
---
include/linux/percpu-refcount.h | 3 ++-
lib/percpu-refcount.c | 4 +---
2 files changed, 3 insertions(+), 4 deletions(-)

--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -67,7 +67,8 @@ struct percpu_ref {
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_and_confirm(struct percpu_ref *ref,
percpu_ref_func_t *confirm_kill);

--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -57,12 +57,10 @@ int percpu_ref_init(struct percpu_ref *r
static void percpu_ref_kill_rcu(struct rcu_head *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;
int cpu;

- pcpu_count = ACCESS_ONCE(ref->pcpu_count);
-
/* Mask out PCPU_REF_DEAD */
pcpu_count = (unsigned __percpu *)
(((unsigned long) pcpu_count) & ~PCPU_STATUS_MASK);