From 1be5d4fa0af34fb7bafa205aeb59f5c7cc7a089d Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 30 Nov 2016 21:04:42 +0000
Subject: [PATCH] locking/rtmutex: Use READ_ONCE() in rt_mutex_owner()
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>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20161130210030.431379999@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/locking/rtmutex_common.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index 4f5f83c7d2d35..e317e1cbb3eba 100644
--- 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);
}
/*
--
GitLab