This is a note to let you know that I've just added the patch titled
locking/rtmutex: Use READ_ONCE() in rt_mutex_owner()
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
locking-rtmutex-use-read_once-in-rt_mutex_owner.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1be5d4fa0af34fb7bafa205aeb59f5c7cc7a089d Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Wed, 30 Nov 2016 21:04:42 +0000
Subject: locking/rtmutex: Use READ_ONCE() in rt_mutex_owner()
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: David Daney <ddaney@xxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Sebastian Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20161130210030.431379999@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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);
}
/*
Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are
queue-4.4/locking-rtmutex-prevent-dequeue-vs.-unlock-race.patch
queue-4.4/perf-x86-fix-full-width-counter-counter-overflow.patch
queue-4.4/locking-rtmutex-use-read_once-in-rt_mutex_owner.patch
--
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