linux-kernel - Re: [ipw3945-devel] 2.6.24-rc5-mm1 -- INFO: possible circular locking dependency detected -- pm-suspend/5800 is trying to acquire lock

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Date:	Wed, 19 Dec 2007 08:10:54 -0500
From:	"Miles Lane" <miles.lane@...il.com>
To:	"Zhu Yi" <yi.zhu@...el.com>
Cc:	"Johannes Berg" <johannes@...solutions.net>,
	"Len Brown" <len.brown@...el.com>, netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	ipw3945-devel@...ts.sourceforge.net,
	"Rafael J. Wysocki" <rjw@...k.pl>, "Pavel Machek" <pavel@...e.cz>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: [ipw3945-devel] 2.6.24-rc5-mm1 -- INFO: possible circular locking dependency detected -- pm-suspend/5800 is trying to acquire lock

On Dec 18, 2007 9:58 PM, Zhu Yi <yi.zhu@...el.com> wrote:
>
> On Tue, 2007-12-18 at 15:57 +0100, Johannes Berg wrote:
> > Thanks. This is a bug in iwlwifi.
> >
> > The problem is actually another case where my workqueue debugging with
> > lockdep is triggering a warning :))
> >
> > Here's the thing:
> >
> > iwl3945_cancel_deferred_work does
> >
> > cancel_delayed_work_sync(&priv->init_alive_start);
> >
> > (which is the "(&(&priv->init_alive_start)->work)" lock)
> >
> > but it is called from within a locked section of
> > mutex_lock(&priv->mutex); (locked from iwl3945_pci_suspend)
> >
> > On the other hand, the task that runs from the init_alive_start
> > workqueue is iwl3945_bg_init_alive_start() which will lock the same
> > mutex.
> >
> > So the deadlock condition is that you can be in
> > cancel_delayed_work_sync() above while the mutex is locked, and be
> > waiting for iwl_3945_bg_init_alive_start() which tries to lock the
> > mutex.
>
> Thanks for the analysis.
>
> Miles, please try the attached patch. I'll send a patch for both 3945
> and 4965 to linux-wireless later.

I tested it and it looks good here.  Thanks!

        Miles
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