[Devel] [PATCH rh7 05/11] percpu-refcount: add __must_check to percpu_ref_init() and don't use ACCESS_ONCE() in percpu_ref_kill_rcu()

[Vladimir Davydov]

From: Tejun Heo <tj at kernel.org>

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 at kernel.org>
(cherry picked from commit acac7883ee7bcc32476963bce7baf73d44574dd1)
Signed-off-by: Vladimir Davydov <vdavydov at parallels.com>
---
 include/linux/percpu-refcount.h | 3 ++-
 lib/percpu-refcount.c           | 4 +---
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index b61bd6f23985..8146aa9cd89e 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -66,7 +66,8 @@ 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(struct percpu_ref *ref);
 
 #define PCPU_STATUS_BITS	2
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 9a78e55fa48f..b35eaac2954f 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -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)
 {
 	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);
-- 
2.1.4