| From | Jiri Slaby <> | Subject | [PATCH 3.12 005/235] locking/rtmutex: Use READ_ONCE() in rt_mutex_owner() | Date | Fri, 27 Jan 2017 11:52:18 +0100 |
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From: Thomas Gleixner <tglx@linutronix.de>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit 1be5d4fa0af34fb7bafa205aeb59f5c7cc7a089d upstream.
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> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: David Daney <ddaney@caviumnetworks.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sebastian Siewior <bigeasy@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Link: http://lkml.kernel.org/r/20161130210030.431379999@linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Jiri Slaby <jslaby@suse.cz> --- kernel/rtmutex_common.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/rtmutex_common.h b/kernel/rtmutex_common.h index 53a66c85261b..1823c094fe96 100644 --- a/kernel/rtmutex_common.h +++ b/kernel/rtmutex_common.h @@ -96,8 +96,9 @@ 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); } /* -- 2.11.0
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