linux-kernel - Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

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Message-ID: <20120216184919.GA1934@redhat.com>
Date:	Thu, 16 Feb 2012 19:49:19 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrey Vagin <avagin@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Alexey Dobriyan <adobriyan@...il.com>, Valdis.Kletnieks@...edu,
	Michal Marek <mmarek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree

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.

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