linux-kernel - [PATCH 1/4] locking/rwsem: Avoid stale ->count for rwsem_down_write

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Message-Id: <1462769770-29363-2-git-send-email-dave@stgolabs.net>
Date:	Sun,  8 May 2016 21:56:07 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	mingo@...nel.org, peterz@...radead.org, tglx@...utronix.de
Cc:	Waiman.Long@....com, jason.low2@...com, dave@...olabs.net,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 1/4] locking/rwsem: Avoid stale ->count for rwsem_down_write_failed()

The field is obviously updated w.o the lock and needs a READ_ONCE
while waiting for lock holder(s) to go away, just like we do with
all other ->count accesses.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 kernel/locking/rwsem-xadd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index df4dcb883b50..7d62772600cf 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -494,7 +494,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
 			}
 			schedule();
 			set_current_state(state);
-		} while ((count = sem->count) & RWSEM_ACTIVE_MASK);
+		} while ((count = READ_ONCE(sem->count)) & RWSEM_ACTIVE_MASK);
 
 		raw_spin_lock_irq(&sem->wait_lock);
 	}
-- 
2.8.1