From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751128AbWG0Ma6 (ORCPT ); Thu, 27 Jul 2006 08:30:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751183AbWG0Ma6 (ORCPT ); Thu, 27 Jul 2006 08:30:58 -0400 Received: from ppsw-7.csi.cam.ac.uk ([131.111.8.137]:34491 "EHLO ppsw-7.csi.cam.ac.uk") by vger.kernel.org with ESMTP id S1751128AbWG0Ma5 (ORCPT ); Thu, 27 Jul 2006 08:30:57 -0400 X-Cam-SpamDetails: Not scanned X-Cam-AntiVirus: No virus found X-Cam-ScannerInfo: http://www.cam.ac.uk/cs/email/scanner/ Subject: Re: [BUG?] possible recursive locking detected From: Anton Altaparmakov To: Nick Piggin Cc: Andrew Morton , eike-kernel@sf-tec.de, linux-kernel@vger.kernel.org, aia21@cantab.net In-Reply-To: <44C88F46.9010201@yahoo.com.au> References: <200607261805.26711.eike-kernel@sf-tec.de> <20060726225311.f51cee6d.akpm@osdl.org> <44C86271.9030603@yahoo.com.au> <1153984527.21849.2.camel@imp.csi.cam.ac.uk> <20060727003806.def43f26.akpm@osdl.org> <1153988398.21849.16.camel@imp.csi.cam.ac.uk> <44C884EF.6010705@yahoo.com.au> <1153992928.21849.41.camel@imp.csi.cam.ac.uk> <44C88F46.9010201@yahoo.com.au> Content-Type: text/plain Organization: Computing Service, University of Cambridge, UK Date: Thu, 27 Jul 2006 13:30:34 +0100 Message-Id: <1154003434.21849.44.camel@imp.csi.cam.ac.uk> Mime-Version: 1.0 X-Mailer: Evolution 2.6.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2006-07-27 at 20:02 +1000, Nick Piggin wrote: > Anton Altaparmakov wrote: > > On Thu, 2006-07-27 at 19:18 +1000, Nick Piggin wrote: > > > >>Anton Altaparmakov wrote: > > >>>I beg to differ. It is a bug. You cannot reenter the file system when > >>>the file system is trying to allocate memory. Otherwise you can never > >>>allocate memory with any locks held or you are bound to introduce an > >>>A->B B->A deadlock somewhere. > >> > >>I don't think it is a bug in general. It really depends on the allocation: > >> > >>- If it is a path that might be required in order to writeout a page, then > >>yes GFP_NOFS is going to help prevent deadlocks. > >> > >>- If it is a path where you'll take the same locks as page reclaim requires, > >>then again GFP_NOFS is required. > >> > >>For NTFS case, it seems like holding i_mutex on the write path falls foul > >>of the second problem. But I agree with Andrew that this is a critical case > >>where we do have to enter the fs. GFP_NOFS is too big a hammer to use. > >> > >>I guess you'd have to change NTFS to do something sane privately, or come > >>up with a nice general solution that doesn't harm the common filesystems > >>that apparently don't have a problem here... can you just add GFP_NOFS to > >>NTFS's mapping_gfp_mask to start with? > > > > > > I don't think NTFS has a problem either. It is a theoretical problem > > No, I mean: *really* doesn't have a problem. If Andrew says ext2 doesn't > need i_mutex in reclaim, then I tend to believe him. > > > with an extremely small chance of being hit. I am happy to have such a > > problem for now. There are more pressing problems to solve. The only > > thing that needs to happen is for the messages to stop so people stop > > complaining / getting worried about them... > > I guess the memory deadlock issue is probably mostly theoretical, although > it is still nice to get them fixed. I'd imagine a deadlock condition -- if > one really exists -- could be hit without much problem though. Page reclaim > will readily get kicked from the write(2) path, and will potentially free > *lots* of stuff from there. > > If it isn't a problem for you, I'd suspect it might be due to some other > conditions which happen to mean it is avoided. For example, the inode who's > i_mutex you are holding will have a raised refcount AFAIK, so it will not > get reclaimed and so may get around your problem. That is true, yes. So at least in that respect it should be safe. > This would be a valid solution IMO. It probably could do with documentation > to outline the issues, though. That is true. Best regards, Anton -- Anton Altaparmakov (replace at with @) Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net WWW: http://www.linux-ntfs.org/ & http://www-stu.christs.cam.ac.uk/~aia21/