From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
David Daney <ddaney@caviumnetworks.com>,
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>,
stable@vger.kernel.org
Subject: Re: [patch 1/4] rtmutex: Prevent dequeue vs. unlock race
Date: Thu, 1 Dec 2016 19:25:42 +0100 [thread overview]
Message-ID: <20161201182542.GP3045@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20161130210030.351136722@linutronix.de>
On Wed, Nov 30, 2016 at 09:04:41PM -0000, Thomas Gleixner wrote:
> It's remarkable that the test program provided by David triggers on ARM64
> and MIPS64 really quick, but it refuses to reproduce on x8664, while the
> problem exists there as well. That refusal might explain that this got not
> discovered earlier despite the bug existing from day one of the rtmutex
> implementation more than 10 years ago.
> - clear_rt_mutex_waiters(lock);
So that compiles into:
andq $0xfffffffffffffffe,0x48(%rbx)
With is a RmW memop. Now per the architecture documents we can decompose
that into a normal load-store and the race exists. But I would not be
surprised if that starts with the cacheline in exclusive mode (because
it knows it will do the store). Which makes it a very tiny race indeed.
next prev parent reply other threads:[~2016-12-01 18:25 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 [this message]
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 ` [patch 2/4] rtmutex: Use READ_ONCE() in rt_mutex_owner() Thomas Gleixner
2016-12-02 10:45 ` [tip:locking/core] locking/rtmutex: " 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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