linux-kernel - [PATCH 1/2] asm-generic: rwsem: ensure sem->cnt is only accessed via atomic_long

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Message-Id: <1393003347-24958-1-git-send-email-will.deacon@arm.com>
Date:	Fri, 21 Feb 2014 17:22:26 +0000
From:	Will Deacon <will.deacon@....com>
To:	linux-kernel@...r.kernel.org
Cc:	rkuo@...eaurora.org, arnd@...db.de, paulus@...ba.org,
	Will Deacon <will.deacon@....com>
Subject: [PATCH 1/2] asm-generic: rwsem: ensure sem->cnt is only accessed via atomic_long_*

The asm-generic rwsem implementation directly acceses sem->cnt when
performing a __down_read_trylock operation. Whilst this is probably safe
on all architectures, we should stick to the atomic_long_* API and use
atomic_long_read instead.

Signed-off-by: Will Deacon <will.deacon@....com>
---
 include/asm-generic/rwsem.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
index bb1e2cdeb9bf..75af612f54f8 100644
--- a/include/asm-generic/rwsem.h
+++ b/include/asm-generic/rwsem.h
@@ -41,7 +41,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 {
 	long tmp;
 
-	while ((tmp = sem->count) >= 0) {
+	while ((tmp = atomic_long_read((atomic_long_t *)&sem->count)) >= 0) {
 		if (tmp == cmpxchg(&sem->count, tmp,
 				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
 			return 1;
-- 
1.8.2.2

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