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

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Message-ID: <46696917.50004@gmail.com>
Date:	Fri, 08 Jun 2007 23:35:03 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Tejun Heo <htejun@...il.com>
CC:	Greg KH <greg@...ah.com>, 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

Tejun Heo wrote:
> 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.

Have been trying to reproduce the problem on the latest -rc but haven't
succeeded yet.  It seems I lost my magic recipe for these races.  Did
anyone succeed?

-- 
tejun
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