Commit c6a5bf4c authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Greg Kroah-Hartman

locking/rtmutex: Use READ_ONCE() in rt_mutex_owner()

commit 1be5d4fa 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: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter 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.deSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b27d9147
...@@ -75,8 +75,9 @@ task_top_pi_waiter(struct task_struct *p) ...@@ -75,8 +75,9 @@ task_top_pi_waiter(struct task_struct *p)
static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock) static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock)
{ {
return (struct task_struct *) unsigned long owner = (unsigned long) READ_ONCE(lock->owner);
((unsigned long)lock->owner & ~RT_MUTEX_OWNER_MASKALL);
return (struct task_struct *) (owner & ~RT_MUTEX_OWNER_MASKALL);
} }
/* /*
......
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