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

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Message-ID: <1349088639.7780.4.camel@twins>
Date:	Mon, 01 Oct 2012 12:50:39 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, mingo@...nel.org
Subject: Re: task_work_add/scheduler_tick: possible circular locking
 dependency detected

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.


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