[PATCH] Fix data race in mark_rt_mutex_waiters

[Hernan Ponce de Leon]

From: Hernan Ponce de Leon <hernanl.leon@xxxxxxxxxx>

Following the defition of data race in
tools/memory-model/linux-kernel.cat the dartagnan tool
https://github.com/hernanponcedeleon/Dat3M
reported a race between mark_rt_mutex_waiters and rt_mutex_cmpxchg_release.

Commit 23f78d4a03c5 ("[PATCH] pi-futex: rt mutex core")
later removed in commit d0aa7a70bf03 ("futex_requeue_pi optimization")
and reverted in commit bd197234b0a6
("Revert "futex_requeue_pi optimization"")

The original commit introduced the data race.

Cc: stable@xxxxxxxxxxxxxxx # v2.6.18.x
Fixes: 23f78d4a03c5 ("[PATCH] pi-futex: rt mutex core")
Signed-off-by: Hernan Ponce de Leon <hernanl.leon@xxxxxxxxxx>
---
 kernel/locking/rtmutex.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 010cf4e6d0b8..7ed9472edd48 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -235,7 +235,7 @@ static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
 	unsigned long owner, *p = (unsigned long *) &lock->owner;
 
 	do {
-		owner = *p;
+		owner = READ_ONCE(*p);
 	} while (cmpxchg_relaxed(p, owner,
 				 owner | RT_MUTEX_HAS_WAITERS) != owner);
 
-- 
2.25.1