Messages in this thread Patch in this message | | | Date | Wed, 30 Nov 2016 21:04:42 -0000 | From | Thomas Gleixner <> | Subject | [patch 2/4] rtmutex: Use READ_ONCE() in rt_mutex_owner() |
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While debugging the rtmutex unlock vs. dequeue race Will suggested to use READ_ONCE() in rt_mutex_owner() as it might race against the cmpxchg_release() in unlock_rt_mutex_safe().
Will: "It's a minor thing which will most likely not matter in practice"
Careful search did not unearth an actual problem in todays code, but it's better to be safe than surprised.
Suggested-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- kernel/locking/rtmutex_common.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/kernel/locking/rtmutex_common.h +++ b/kernel/locking/rtmutex_common.h @@ -75,8 +75,9 @@ task_top_pi_waiter(struct task_struct *p static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock) { - return (struct task_struct *) - ((unsigned long)lock->owner & ~RT_MUTEX_OWNER_MASKALL); + unsigned long owner = (unsigned long) READ_ONCE(lock->owner); + + return (struct task_struct *) (owner & ~RT_MUTEX_OWNER_MASKALL); } /*
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