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

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Message-ID: <4B6BE6BC.4070506@redhat.com>
Date:	Fri, 05 Feb 2010 17:37:00 +0800
From:	Cong Wang <amwang@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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

Eric W. Biederman wrote:
> 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:
> 
> The interesting case is the cpu hotplug is actually a problem.  It isn't
> useful to get a complaint about the non-problems code paths triggered
> by pm.  However my earlier review spotted a real deadlock case.  Where
> in one of the sysfs attributes we iterate over the list of online cpus
> and that appeared to an attribute that removing a cpu would remove
> from sysfs...
> 

You are referring this one:
http://marc.info/?l=linux-kernel&m=126474021428905&w=2
?

Hmm, yeah, I missed that the lock it is holding is not s_active, thus so
not be the case we are trying to fix here.

Thanks for pointing this out.
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