From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031260AbXDUOex (ORCPT ); Sat, 21 Apr 2007 10:34:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1031267AbXDUOex (ORCPT ); Sat, 21 Apr 2007 10:34:53 -0400 Received: from mx1.suse.de ([195.135.220.2]:39576 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031260AbXDUOex (ORCPT ); Sat, 21 Apr 2007 10:34:53 -0400 Message-ID: <462A2107.6060902@suse.de> Date: Sat, 21 Apr 2007 10:34:47 -0400 From: Jeff Mahoney User-Agent: Thunderbird 1.5.0.10 (X11/20060911) MIME-Version: 1.0 To: Jeff Mahoney Cc: a.righi@cineca.it, Andrew Morton , "Vladimir V. Saveliev" , linux-kernel@vger.kernel.org, reiserfs-dev@namesys.com, Edward Shishkin , zam@clusterfs.com, ak@suse.de Subject: Re: Fwd: Fw: [2.6.20.4] BUG: dentry xattrs still in use in shrink_dcache_for_umount() with reiserfs References: <20070413095219.02075323.akpm@linux-foundation.org> <462536B2.5060308@users.sourceforge.net> <200704181816.21166.vs@namesys.com> <46263270.9010108@suse.com> <20070420170738.e269fcae.akpm@linux-foundation.org> <46296CB8.3090100@suse.com> <462A0F06.9020602@cineca.it> <462A2055.1040509@suse.com> In-Reply-To: <462A2055.1040509@suse.com> X-Enigmail-Version: 0.94.0.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Jeff Mahoney wrote: > Andrea Righi wrote: >> Jeff Mahoney wrote: >>> I have the patchset that I mentioned, but I'm not proposing it for 2.6.21. >>> It's much too invasive to be introduced in an -rc7, but it does include >>> locking changes that I believe avoid this bug. >>> >>> Vladimir was right in his analysis that sometimes get_xa_root() takes the >>> reference once and other times twice, but not for the right reasons. I save >>> a reference to the xattr dir to avoid a lookup later, but when there are multiple >>> getxattrs or listxattrs as the first xattr operation on the file system, we can end >>> up taking a second reference when we shouldn't. This is because those operations >>> are protected by read locks and the ->xattr_root pointer isn't protected by anything >>> else. A quick fix would be to just extend the protection of the priv root's i_mutex >>> around the assignment, and test first. The right fix involves a complete rework of >>> the locking, and I have code to do that, it's just too late to include it in 2.6.21. >>> >>> I'd love to know what Andrea (and now Andi Kleen) are doing to hit this now. There >>> haven't been any changes in this code in a while, and the shrink_dcache_for_umount() >>> has been around since October. I'm unable to reproduce locally so far, so if Andrea >>> or Andi could see if this fixes it for them, I'd appreciate it. >> Jeff, your patch doesn't resolve, but you hit the problem. Actually, I >> think the xattr_root pointer must be protected also in get_xa_root() >> using the same private root i_mutex. >> >> I've tested the following patch and it resolves in my case. What do you >> think about it? could it be a reasonable fix? > > Your patch fixes the problem. That'll teach me to spin a patch up while I'm headed > out the door. I think a cleaner solution for now is just to refactor get_xa_root, > __get_xa_root, and create_xa_root into one function to simplify the lookup and the > locking. I think I'll add another step to my patch set that removes the caching of > xattr_root entirely or creates in on mount, as the priv root is created. The privroot > must be cached to avoid a deadlock on the fs-root directory's i_mutex, but xattr_root > was cached as an optimzation. If we need to take privroot->i_mutex every time, there's > no point in caching it since it will probably be in the dcache anyway. > > -Jeff > Ignore this patch. I missed a spot. - -Jeff - -- Jeff Mahoney SUSE Labs -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iD8DBQFGKiEHLPWxlyuTD7IRApRTAJ0WeJzkH7julSus9iqx+LYoAAlFOwCfahu0 4qN7BR/monh7ZcQWZ7Vmz3Y= =UNNw -----END PGP SIGNATURE-----