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

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Date:	Tue, 18 Dec 2007 15:57:06 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Miles Lane <miles.lane@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	ipw3945-devel@...ts.sourceforge.net,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@...e.cz>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: 2.6.24-rc5-mm1 -- INFO: possible circular locking dependency
	detected -- pm-suspend/5800 is trying to acquire lock


> Sorry.  GMail doesn't support sending unwrapped text, as far as I can
> tell.  I will send the log segment to you as an attachment.  Also,
> when I sent my .config inline to Andrew recently, it tripped his spam
> filter.  I'll attach it as well.

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.

johannes

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