linux-kernel - Re: [PATCH] sysfs: differentiate between locking links and non-links

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Date:	Wed, 10 Feb 2010 11:12:18 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Neil Brown <neilb@...e.de>, "Eric W ." <ebiederm@...ssion.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysfs: differentiate between locking links and non-links

On Wed, Feb 10, 2010 at 10:19 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On 02/10/2010 11:08 AM, Américo Wang wrote:
>> This bug report is new for me. Recently we received lots of sysfs lockdep
>> warnings, I am working on a patch to fix all the bogus ones.
>>
>> However, this one is _not_ similar to the other cases, as you decribed.
>> This patch could fix the problem, but not a good fix, IMO. We need more
>> work in sysfs layer to fix this kind of things. I will take care of this.
>
> Can't we just give each s_active lock a separate class?  Would that be
> too costly?
>

Not because it is expensive or not, it is because whether it hits the real
problem.

What I am doing is trying to add a "mutable" flag to sysfs files, those files
could be removed from kernel during some changes, e.g. cpu hotplug, I/O
scheduler switch. I add a new lockdep class for all of them, so that will be
safe for all cases like this.

If I understand this case correctly, it is not that different with the
rest cases
that I met, thus should be included into my fix.

Thanks.
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