From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: David Daney <ddaney@caviumnetworks.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Sebastian Siewior <bigeasy@linutronix.de>,
Will Deacon <will.deacon@arm.com>,
Mark Rutland <mark.rutland@arm.com>
Subject: [patch 2/4] rtmutex: Use READ_ONCE() in rt_mutex_owner()
Date: Wed, 30 Nov 2016 21:04:42 -0000 [thread overview]
Message-ID: <20161130210030.431379999@linutronix.de> (raw)
In-Reply-To: 20161130205431.629977871@linutronix.de
[-- Attachment #1: rtmutex--Use-READ_ONCE---in-rt_mutex_owner--.patch --]
[-- Type: text/plain, Size: 1010 bytes --]
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>
---
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);
}
/*
next prev parent reply other threads:[~2016-11-30 21:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-30 21:04 [patch 0/4] rtmutex: Plug unlock vs. requeue race Thomas Gleixner
2016-11-30 21:04 ` [patch 1/4] rtmutex: Prevent dequeue vs. unlock race Thomas Gleixner
2016-12-01 17:56 ` David Daney
2016-12-01 18:25 ` Peter Zijlstra
2016-12-02 8:18 ` Thomas Gleixner
2016-12-02 0:53 ` Steven Rostedt
2016-12-02 10:45 ` [tip:locking/core] locking/rtmutex: " tip-bot for Thomas Gleixner
2016-11-30 21:04 ` Thomas Gleixner [this message]
2016-12-02 10:45 ` [tip:locking/core] locking/rtmutex: Use READ_ONCE() in rt_mutex_owner() tip-bot for Thomas Gleixner
2016-11-30 21:04 ` [patch 3/4] rtmutex: Get rid of RT_MUTEX_OWNER_MASKALL Thomas Gleixner
2016-12-02 10:46 ` [tip:locking/core] locking/rtmutex: " tip-bot for Thomas Gleixner
2016-11-30 21:04 ` [patch 4/4] rtmutex: Explain locking rules for rt_mutex_proxy_unlock()/init_proxy_locked() Thomas Gleixner
2016-12-02 10:46 ` [tip:locking/core] locking/rtmutex: " tip-bot for Thomas Gleixner
2016-12-01 18:33 ` [patch 0/4] rtmutex: Plug unlock vs. requeue race Peter Zijlstra
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