linux-kernel - Re: task_work_add/scheduler_tick: possible circular locking dependency detected

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Message-ID: <20121001115936.GA17830@localhost>
Date:	Mon, 1 Oct 2012 19:59:36 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>, mingo@...nel.org
Subject: Re: task_work_add/scheduler_tick: possible circular locking
 dependency detected

On Mon, Oct 01, 2012 at 12:50:39PM +0200, Peter Zijlstra wrote:
> On Fri, 2012-09-28 at 19:34 +0800, Fengguang Wu wrote:
> > Peter,
> > 
> > I got the warning
> > 
> > [   10.412023] 
> > [   10.412611] ======================================================
> > [   10.413014] [ INFO: possible circular locking dependency detected ]
> > [   10.413014] 3.6.0-rc4-00098-g7eaffe9 #402 Not tainted
> > [   10.413014] -------------------------------------------------------
> > [   10.413014] init/1 is trying to acquire lock:
> > [   10.413014]  (&p->pi_lock){-.-.-.}, at: [<ffffffff81088214>] task_work_add+0x28/0x82
> > [   10.413014] 
> > [   10.413014] but task is already holding lock:
> > [   10.413014]  (&rq->lock){-.-.-.}, at: [<ffffffff8109c6ea>] scheduler_tick+0x3f/0xec
> > [   10.413014] 
> > [   10.413014] which lock already depends on the new lock.
> > [   10.413014] 
> > [   10.413014] 
> > 
> 
> The commit ac3d0da8f3290b3d394cdb7f50604424a7cd6092 should avoid this
> from happening, not sure what branch its on, but it was in tip before
> all this landed, so I guess its due to you testing sched/numa branch and
> not a merged branch like master or auto-next.

Peter, you are right, it's tested in tip:sched/numa. linux-next is
fine. Hmm, I should automatically test linux-next before raising the
problem, hehe.

Thanks,
Fengguang
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