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Subject[PATCH] Fix data race in mark_rt_mutex_waiters
Date
From: Hernan Ponce de Leon <hernanl.leon@huawei.com>

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@vger.kernel.org # v2.6.18.x
Fixes: 23f78d4a03c5 ("[PATCH] pi-futex: rt mutex core")
Signed-off-by: Hernan Ponce de Leon <hernanl.leon@huawei.com>
---
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
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