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Date: Wed, 7 Jan 2009 19:50:09 +0530
From: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>, Linux Kernel <linux-kernel@vger.kernel.org>,
       Balbir Singh <balbir@linux.vnet.ibm.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Mike Galbraith <efault@gmx.de>
Subject: Re: [BUG] 2.6.28-git LOCKDEP: Possible recursive rq->lock
Message-ID: <20090107142009.GM4574@dirshya.in.ibm.com>
Reply-To: svaidy@linux.vnet.ibm.com
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* Peter Zijlstra <a.p.zijlstra@chello.nl> [2009-01-07 14:12:43]:

> On Wed, 2009-01-07 at 17:59 +0530, Vaidyanathan Srinivasan wrote:
> 
> > =============================================
> > [ INFO: possible recursive locking detected ]
> > 2.6.28-autotest-tip-sv #1
> > ---------------------------------------------
> > klogd/5062 is trying to acquire lock:
> >  (&rq->lock){++..}, at: [<ffffffff8022aca2>] task_rq_lock+0x45/0x7e
> > 
> > but task is already holding lock:
> >  (&rq->lock){++..}, at: [<ffffffff805f7354>] schedule+0x158/0xa31
> > 
> > other info that might help us debug this:
> > 1 lock held by klogd/5062:
> >  #0:  (&rq->lock){++..}, at: [<ffffffff805f7354>] schedule+0x158/0xa31
> > 
> > stack backtrace:
> > Pid: 5062, comm: klogd Not tainted 2.6.28-autotest-tip-sv #1
> > Call Trace:
> >  [<ffffffff80259ef1>] __lock_acquire+0xeb9/0x16a4
> >  [<ffffffff8025a6c0>] ? __lock_acquire+0x1688/0x16a4
> >  [<ffffffff8025a761>] lock_acquire+0x85/0xa9
> >  [<ffffffff8022aca2>] ? task_rq_lock+0x45/0x7e
> >  [<ffffffff805fa4d4>] _spin_lock+0x31/0x66
> >  [<ffffffff8022aca2>] ? task_rq_lock+0x45/0x7e
> >  [<ffffffff8022aca2>] task_rq_lock+0x45/0x7e
> >  [<ffffffff80233363>] try_to_wake_up+0x88/0x27a
> >  [<ffffffff80233581>] wake_up_process+0x10/0x12
> >  [<ffffffff805f775c>] schedule+0x560/0xa31
> 
> I'd be most curious to know where in schedule we are.

ok, we are in sched.c:3777

                double_unlock_balance(this_rq, busiest);
                if (active_balance)
>>>>>>>>>>>              wake_up_process(busiest->migration_thread);

        } else  

In active balance in newidle.  This implies sched_mc was 2 at that time.
let me trace this and debug further.

--Vaidy

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