linux-kernel - Re: [Patch v2] sysfs: add lockdep class support to s

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Date:	Fri, 05 Feb 2010 00:57:12 -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>,
	Peter Zijlstra <peterz@...radead.org>,
	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 v2] sysfs: add lockdep class support to s_active

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. Based on his work and Peter's suggestion, I write this patch,
> hopefully we can fix the warning completely.
>
> This patch put sysfs s_active into two classes, one is for PM, the other
> is for the rest, so lockdep will distinguish them.
>
> 1. http://lkml.org/lkml/2010/1/10/282

What testing has this patch seen?

In particular does this work to actually clear up the pm case?

Eric
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