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

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Date:	Sun, 10 Jun 2007 09:18:47 -0700
From:	Greg KH <greg@...ah.com>
To:	Tejun Heo <htejun@...il.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

On Sat, Jun 09, 2007 at 03:49:46PM +0900, Tejun Heo wrote:
> Tejun Heo wrote:
> > 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?
> 
> Alright, overnight test finally hit the race condition.  It takes me
> much longer now but the race condition is definitely still there.  I'll
> verify each proposed patch and send it for 2.6.22 inclusion and if
> they're accepted to -stable.

Ok, thanks for doing this.

greg k-h
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