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

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Date:	Mon, 15 Feb 2010 14:35:37 +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>,
	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

Eric W. Biederman wrote:
> 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.
> 

(Sorry for the delay, we are having Chinese new year here.)

Oh, yes, I just worried that if my patch is aggressive.
I saw your patch, will have a review now.

Thank you!

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