linux-kernel - Re: [RFC Patch] sysfs: add marks for mutable sysfs files

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Date:	Wed, 10 Feb 2010 09:51:24 -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>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Miles Lane <miles.lane@...il.com>,
	Larry Finger <Larry.Finger@...inger.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	akpm@...ux-foundation.org
Subject: Re: [RFC Patch] sysfs: add marks for mutable sysfs files

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

> NOTE: This patch is only a draft, not ready to be taken.
>
> This fixes all the s_active related bogus lockdep warnings that I received,
> I already tested it, it works fine for cpu hotplug, I/O scheduler switch,
> and suspend.
>
> This patch introduces sever sysfs/kobject interfaces to add mutable
> sysfs files or kobjects, those files could be removed by the kernel
> during some event, e.g. cpu hotplug. All of this kind of sysfs files
> should use these API's, to avoid the deadlock warnings.
>
> I am still not sure if this is the best fix.
>
> Please comment.

mutable as you describe it happens to be the common case, and that
class of files is not free from this class of problem.

Your patch is actively wrong if it solves the i/o scheduler issue,
as those files are in fact mutable by your definition, block devices
are hot pluggable.

Having a special case for permanent sysfs files, that we refuse to
delete would be reasonable, but it certainly does not cover
everything.

Eric
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