4.8-stable review patch. If anyone has any objections, please let me know.
------------------ From: Thomas Gleixner <t...@linutronix.de> 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.dea...@arm.com> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: David Daney <dda...@caviumnetworks.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Mark Rutland <mark.rutl...@arm.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Sebastian Siewior <bige...@linutronix.de> Cc: Steven Rostedt <rost...@goodmis.org> Link: http://lkml.kernel.org/r/20161130210030.431379...@linutronix.de Signed-off-by: Ingo Molnar <mi...@kernel.org> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- 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); } /*
