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Date: Thu, 16 Feb 2012 19:49:19 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Vasiliy Kulikov <segoon@openwall.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        Andrey Vagin <avagin@openvz.org>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Glauber Costa <glommer@parallels.com>,
        Andi Kleen <andi@firstfloor.org>, Tejun Heo <tj@kernel.org>,
        Matt Helsley <matthltc@us.ibm.com>, Pekka Enberg <penberg@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Alexey Dobriyan <adobriyan@gmail.com>, Valdis.Kletnieks@vt.edu,
        Michal Marek <mmarek@suse.cz>,
        Frederic Weisbecker <fweisbec@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree
Message-ID: <20120216184919.GA1934@redhat.com>
References: <20120215195610.GJ4533@moon> <20120215195733.GA8021@albatros> <20120215200533.GQ1894@moon> <20120215202538.GK4533@moon> <20120215210934.GL4533@moon> <20120215215807.GM4533@moon> <20120216144954.GA11953@redhat.com> <20120216151340.GI1905@moon> <20120216164901.GD3849@moon> <20120216182106.GA17020@albatros>
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On 02/16, Vasiliy Kulikov wrote:
>
> On Thu, Feb 16, 2012 at 20:49 +0400, Cyrill Gorcunov wrote:
> > +	err = mutex_lock_killable(m1);
> > +	if (!err && likely(m1 != m2)) {
> > +		err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING);
>
> Doesn't it lead to a deadlock?
>
> mutex_lock_killable(task1)
> |					mutex_lock_killable(task2)
> mutex_lock_killable_nested(task2)	|
> (locked)				|
> 					mutex_lock_killable_nested(task1)
> 					(locked)

Please note the

	if (m1 >= m2)
		swap(m1. m2)

at the start.

Oleg.