linux-kernel - Re: [Patch 0/2] sysfs: fix s

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Date:	Thu, 28 Jan 2010 23:21:46 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Amerigo Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Miles Lane <miles.lane@...il.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Larry Finger <Larry.Finger@...inger.net>,
	akpm@...ux-foundation.org
Subject: Re: [Patch 0/2] sysfs: fix s_active lockdep warning

Amerigo Wang <amwang@...hat.com> writes:

> Recently we met a lockdep warning from sysfs during s2ram or cpu hotplug.
> As reported by several people, it is something like:
>
> [ 6967.926563] ACPI: Preparing to enter system sleep state S3
> [ 6967.956156] Disabling non-boot CPUs ...
> [ 6967.970401]
> [ 6967.970408] =============================================
> [ 6967.970419] [ INFO: possible recursive locking detected ]
> [ 6967.970431] 2.6.33-rc2-git6 #27
> [ 6967.970439] ---------------------------------------------
> [ 6967.970450] pm-suspend/22147 is trying to acquire lock:
> [ 6967.970460]  (s_active){++++.+}, at: [<c10d2941>]
> sysfs_hash_and_remove+0x3d/0x4f
> [ 6967.970493]
> [ 6967.970497] but task is already holding lock:
> [ 6967.970506]  (s_active){++++.+}, at: [<c10d4110>]
> sysfs_get_active_two+0x16/0x36
> [...]
>
> Eric already provides a patch for this[1], but it still can't fix the
> problem. I add the missing part of Eric's patch and send these two patches
> together, hopefully we can fix the warning completely.
>
> 1. http://lkml.org/lkml/2010/1/10/282
>
>
> Reported-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Reported-by: Larry Finger <Larry.Finger@...inger.net>
> Reported-by: Miles Lane <miles.lane@...il.com>
> Reported-by: Heiko Carstens <heiko.carstens@...ibm.com>
> Signed-off-by: WANG Cong <amwang@...hat.com>
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Greg Kroah-Hartman <gregkh@...e.de>

Thanks for following up on this.

I suspect we may want to create a separate class for each sysfs file
instead of playing whack-a-mole and creating a subclass each time we
have problems.

I don't see why the rules for one sysfs file should be the same as for
any other sysfs file.

Eric

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