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To: Amerigo Wang <amwang@redhat.com>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
       Greg Kroah-Hartman <gregkh@suse.de>,
       Peter Zijlstra <peterz@infradead.org>,
       Miles Lane <miles.lane@gmail.com>,
       Heiko Carstens <heiko.carstens@de.ibm.com>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Larry Finger <Larry.Finger@lwfinger.net>, akpm@linux-foundation.org
Subject: Re: [Patch v2] sysfs: add lockdep class support to s_active
References: <20100205064622.4141.72867.sendpatchset@localhost.localdomain>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: Fri, 05 Feb 2010 00:57:12 -0800
In-Reply-To: <20100205064622.4141.72867.sendpatchset@localhost.localdomain> (Amerigo Wang's message of "Fri\, 5 Feb 2010 01\:42\:56 -0500")
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Amerigo Wang <amwang@redhat.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