linux-kernel - Re: 2.6.18.4: flush_workqueue calls mutex

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Message-Id: <1166013678.5695.26.camel@lade.trondhjem.org>
Date:	Wed, 13 Dec 2006 07:41:18 -0500
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	xb <xavier.bru@...l.net>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.18.4: flush_workqueue calls mutex_lock in interrupt
	environment

On Wed, 2006-12-13 at 09:02 +0100, Arjan van de Ven wrote:
> On Wed, 2006-12-13 at 08:25 +0100, xb wrote:
> > Hi all,
> > 
> > Running some IO stress tests on a 8*ways IA64 platform, we got:
> >      BUG: warning at kernel/mutex.c:132/__mutex_lock_common()  message
> > followed by:
> >      Unable to handle kernel paging request at virtual address
> > 0000000000200200
> > oops corresponding to anon_vma_unlink() calling list_del() on a
> > poisonned list.
> > 
> > Having a look to the stack, we see that flush_workqueue() calls
> > mutex_lock() with softirqs disabled.
> 
> something is wrong here... flush_workqueue() is a sleeping function and
> is not allowed to be called in such a context!

It seems utterly insane to have aio_complete() flush a workqueue. That
function has to be called from a number of different environments,
including non-sleep tolerant environments.

For instance it means that directIO on NFS will now cause the rpciod
workqueues to call flush_workqueue(aio_wq), thus slowing down all RPC
activity.

Trond

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