linux-kernel - Re: [PATCH] reiserfs: fix xattr root locking/refcount bug

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Message-ID: <462B38D7.1060000@cineca.it>
Date:	Sun, 22 Apr 2007 12:28:40 +0200 (MEST)
From:	Andrea Righi <a.righi@...eca.it>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Jeff Mahoney <jeffm@...e.com>
Cc:	"Vladimir V. Saveliev" <vs@...esys.com>,
	linux-kernel@...r.kernel.org, reiserfs-dev@...esys.com,
	Edward Shishkin <edward@...esys.com>, zam@...sterfs.com,
	ak@...e.de
Subject: Re: [PATCH] reiserfs: fix xattr root locking/refcount bug

Andrew Morton wrote:
> On Sat, 21 Apr 2007 11:26:31 -0400 Jeff Mahoney <jeffm@...e.com> wrote:
> 
>>  The listxattr() and getxattr() operations are only protected by a read
>>  lock. As a result, if either of these operations run in parallel, a race
>>  condition exists where the xattr_root will end up being cached twice,
>>  which results in the leaking of a reference and a BUG() on umount.
>>
>>  This patch refactors get_xa_root(), __get_xa_root(), and
>>  create_xa_root(), into one get_xa_root() function that takes
>>  the appropriate locking around the entire critical section.
> 
> Great, thanks.
> 
> Now we need to work out the timing.  Our options are to shove
> it into 2.6.21 immediately, or to give it a run in 2.6.22-rc1 then
> backport into 2.6.21.x.
> 
> What is everyone's confidence level?
> 

Tested the patch and I confirm that it fixes the problem. Regarding the
confidence level, in my case I can say that on a suse 10.0 I can always
reproduce the bug on every shutdown. Anyway, I'm not using the default
kernel shipped with suse 10.0, but maybe the same bug could be seen in
opensuse 10.3 that (if I'm not wrong) uses a 2.6.20.

BTW there are not enough details, but a similar problem seems to be
already reported here: https://bugzilla.novell.com/show_bug.cgi?id=259215

-Andrea
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