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

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Message-ID: <462BCA74.5020109@suse.com>
Date:	Sun, 22 Apr 2007 16:49:56 -0400
From:	Jeff Mahoney <jeffm@...e.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	a.righi@...eca.it, "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

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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?

I'm pretty confident in this patch for 2.6.21, but I wouldn't object to
waiting until 2.6.22-rc1 either. Operationally, the change isn't that
big and makes the locking more clear and the code simpler. I've tested
on populated file systems, virgin file systems, and tested the error
handling path with each. There is still a bug lurking in how a failure
in ACL inheritance is cleaned up that I ran into while testing, but this
patch didn't introduce it or exacerbate it. I'll add that to my xattr
patch queue.

- -Jeff

- --
Jeff Mahoney
SUSE Labs
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