linux-kernel - Re: INFO: possible circular locking dependency at cleanup_workqueue

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Message-Id: <1242809103.19216.2.camel@johannes.local>
Date:	Wed, 20 May 2009 10:45:03 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: INFO: possible circular locking dependency at 
 cleanup_workqueue_thread

On Wed, 2009-05-20 at 16:21 +0800, Ming Lei wrote:

> For me, the real puzzle is that  how lockdep introduce  #3
> (dpm_list_mtx){+.+.+.}
> 
> -> #3 (dpm_list_mtx){+.+.+.}:
>       [<ffffffff80271a64>] __lock_acquire+0xc64/0x10a0
>       [<ffffffff80271f38>] lock_acquire+0x98/0x140
>       [<ffffffff8054e78c>] __mutex_lock_common+0x4c/0x3b0
>       [<ffffffff8054ebf6>] mutex_lock_nested+0x46/0x60
>       [<ffffffff804532ff>] device_pm_add+0x1f/0xe0
>       [<ffffffff8044b9bf>] device_add+0x45f/0x570
>       [<ffffffffa007c578>] wiphy_register+0x158/0x280 [cfg80211]
>       [<ffffffffa017567c>] ieee80211_register_hw+0xbc/0x410 [mac80211]
>       [<ffffffffa01f7c5c>] iwl3945_pci_probe+0xa1c/0x1080 [iwl3945]
>       [<ffffffff803c4307>] local_pci_probe+0x17/0x20
>       [<ffffffff803c5458>] pci_device_probe+0x88/0xb0
>       [<ffffffff8044e1e9>] driver_probe_device+0x89/0x180
>       [<ffffffff8044e37b>] __driver_attach+0x9b/0xa0
>       [<ffffffff8044d67c>] bus_for_each_dev+0x6c/0xa0
>       [<ffffffff8044e03e>] driver_attach+0x1e/0x20
>       [<ffffffff8044d955>] bus_add_driver+0xd5/0x290
>       [<ffffffff8044e668>] driver_register+0x78/0x140
>       [<ffffffff803c56f6>] __pci_register_driver+0x66/0xe0
>       [<ffffffffa00bd05c>] 0xffffffffa00bd05c
>       [<ffffffff8020904f>] do_one_initcall+0x3f/0x1c0
>       [<ffffffff8027d071>] sys_init_module+0xb1/0x200
>       [<ffffffff8020c15b>] system_call_fastpath+0x16/0x1b
>       [<ffffffffffffffff>] 0xffffffffffffffff
> 
> into the lockdep graph?  in which process context?  and what is the
> previous held lock?
> After all, there is a path ( #0,#1,#2,...,#5 ) in the directed graph
> and #3 is added by
> add_lock_to_list().

Well, as Peter explained in the other part of the thread, lockdep will
always show the first cycle it found, not the shortest. The scenario
that I outlined is actually closer to this report:
http://paste.pocoo.org/show/116240/ but not quite that either, I further
shortened it.

Anyway, I have no idea how to fix it.

johannes

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