Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761561AbYGODTS (ORCPT ); Mon, 14 Jul 2008 23:19:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755936AbYGODTH (ORCPT ); Mon, 14 Jul 2008 23:19:07 -0400 Received: from ipmail01.adl6.internode.on.net ([203.16.214.146]:55554 "EHLO ipmail01.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755806AbYGODTG (ORCPT ); Mon, 14 Jul 2008 23:19:06 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: ApoEAHy0e0h5LFxA/2dsb2JhbACsMQ X-IronPort-AV: E=Sophos;i="4.30,363,1212330600"; d="scan'208";a="149216213" Date: Tue, 15 Jul 2008 13:18:40 +1000 From: Dave Chinner To: Lachlan McIlroy Cc: Mikael Abrahamsson , linux-kernel@vger.kernel.org, xfs@oss.sgi.com, linux-mm@kvack.org Subject: Re: xfs bug in 2.6.26-rc9 Message-ID: <20080715031840.GB29319@disturbed> Mail-Followup-To: Lachlan McIlroy , Mikael Abrahamsson , linux-kernel@vger.kernel.org, xfs@oss.sgi.com, linux-mm@kvack.org References: <20080711084248.GU29319@disturbed> <487B019B.9090401@sgi.com> <20080714121332.GX29319@disturbed> <487C07A4.70202@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <487C07A4.70202@sgi.com> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1552 Lines: 36 On Tue, Jul 15, 2008 at 12:12:52PM +1000, Lachlan McIlroy wrote: > Dave Chinner wrote: >> On Mon, Jul 14, 2008 at 05:34:51PM +1000, Lachlan McIlroy wrote: >>> This is a race between xfs_fsr and a mmap write. xfs_fsr acquires the >>> iolock and then flushes the file and because it has the iolock it doesn't >>> expect any new delayed allocations to occur. A mmap write can allocate >>> delayed allocations without acquiring the iolock so is able to get in >>> after the flush but before the ASSERT. >> >> Christoph and I were contemplating this problem with ->page_mkwrite >> reecently. The problem is that we can't, right now, return an >> EAGAIN-like error to ->page_mkwrite() and have it retry the >> page fault. Other parts of the page faulting code can do this, >> so it seems like a solvable problem. >> >> The basic concept is that if we can return a EAGAIN result we can >> try-lock the inode and hold the locks necessary to avoid this race >> or prevent the page fault from dirtying the page until the >> filesystem is unfrozen. > Why do we need to try-lock the inode? Will we have an ABBA deadlock > if we block on the iolock in ->page_mkwrite()? Yes. With the mmap_sem. Look at the rules in mm/filemap.c and replace i_mutex with iolock.... Cheers, Dave. -- Dave Chinner david@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/