linux-kernel - Re: [PATCH 2/2] sysfs: fix race condition around sd->s

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Message-ID: <4653F98A.8080308@gmail.com>
Date:	Wed, 23 May 2007 10:21:30 +0200
From:	Tejun Heo <htejun@...il.com>
To:	Greg KH <greg@...ah.com>
CC:	Maneesh Soni <maneesh@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Clemens Schwaighofer <cs@...uila.co.jp>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Chuck Ebbert <cebbert@...hat.com>
Subject: Re: [PATCH 2/2] sysfs: fix race condition around sd->s_dentry,	take#2

Greg KH wrote:
> On Mon, May 21, 2007 at 10:31:01AM +0530, Maneesh Soni wrote:
>> On Thu, May 17, 2007 at 08:16:10PM +0200, Tejun Heo wrote:
>>> Allowing attribute and symlink dentries to be reclaimed means
>>> sd->s_dentry can change dynamically.  However, updates to the field
>>> are unsynchronized leading to race conditions.  This patch adds
>>> sysfs_lock and use it to synchronize updates to sd->s_dentry.
>>>
>>> Due to the locking around ->d_iput, the check in sysfs_drop_dentry()
>>> is complex.  sysfs_lock only protect sd->s_dentry pointer itself.  The
>>> validity of the dentry is protected by dcache_lock, so whether dentry
>>> is alive or not can only be tested while holding both locks.
>>>
>>> This is minimal backport of sysfs_drop_dentry() rewrite in devel
>>> branch.
>>>
>>> DONT APPLY JUST YET
>> Looks ok to me.. I have tested it it but unfortunately I couldn't
>> recreate the race without the patch also. It would be helpful if
>> people actually seeing the race, provide the test results.
>>
>> Greg, please merge this one once we have some test results.
> 
> Can someone just resend it after those test results are in, with the
> proper signed-off-by, so I know it's safe to apply?

I'll resend with S-O-B after someone verifies it fixes the problem.

-- 
tejun
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