From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161261AbWI2B2b (ORCPT ); Thu, 28 Sep 2006 21:28:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161263AbWI2B2b (ORCPT ); Thu, 28 Sep 2006 21:28:31 -0400 Received: from mga07.intel.com ([143.182.124.22]:38806 "EHLO azsmga101.ch.intel.com") by vger.kernel.org with ESMTP id S1161261AbWI2B23 (ORCPT ); Thu, 28 Sep 2006 21:28:29 -0400 X-ExtLoop1: 1 X-IronPort-AV: i="4.09,232,1157353200"; d="scan'208"; a="124569674:sNHT1486284415" Subject: Re: [PATCH] Fix commit of ordered data buffers From: "Zhang, Yanmin" To: Jan Kara Cc: akpm@osdl.org, LKML , Badari Pulavarty , ia64 Fedora Core Development In-Reply-To: <20060928213558.GC15478@atrey.karlin.mff.cuni.cz> References: <20060911210530.GA28445@atrey.karlin.mff.cuni.cz> <1159432266.20092.700.camel@ymzhang-perf.sh.intel.com> <20060928213558.GC15478@atrey.karlin.mff.cuni.cz> Content-Type: text/plain Message-Id: <1159493244.20092.718.camel@ymzhang-perf.sh.intel.com> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.5 (1.4.5-9) Date: Fri, 29 Sep 2006 09:27:25 +0800 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2006-09-29 at 05:35, Jan Kara wrote: > Hello, > > > On Tue, 2006-09-12 at 05:05, Jan Kara wrote: > > > Hi Andrew, > > > > > > here is the patch that came out of the thread "set_page_buffer_dirty > > > should skip unmapped buffers". It fixes several flaws in the code > > > writing out ordered data buffers during commit. It definitely fixed the > > > problem Badari was seeing with fsx-linux test. Could you include it > > > into -mm? Since there are quite complex interactions with other JBD code > > > and the locking is kind of ugly, I'd leave it in -mm for a while whether > > > some bug does not emerge ;). Thanks. > > > > > > Honza > > The fsx-linux test issue is a race between journal_commit_transaction > > and journal_dirty_data. After journal_commit_transaction adds buffer_head pointers > > to wbuf, it might unlock journal->j_list_lock. Although all buffer head in wbuf are locked, > > does that prevent journal_dirty_data from unlinking the buffer head from the transaction > > and fsx-linux from truncating it? > Yes, it does. Because the buffers are locked *and dirty*. Nothing can > clear the dirty bit while we are holding the lock and > journal_dirty_data() also waits until it can safely write out the buffer > - which is after we release the buffer lock. With your patch, it's not true because journal_submit_data_buffers clear the dirty flag, so later journal_dirty_data won't try to lock/flush the buffer. journal_dirty_data would just move the jh to the t_sync_datalist of a new transaction. > > > I'm not a journal expert. But I want to discuss it. > > > > My investigation is below (Scenario): > > > > fsx-linux starts journal_dirty_data and journal_dirty_data links a jh to > > journal->j_running_transaction's t_sync_datalist, kjournald might not > > write the buffer to disk quickly, but saves it to array wbuf. > > Then, fsx-linux starts the second journal_dirty_data of a new transaction > > might submit the same buffer head and move the jh to the new transaction's > > t_sync_datalist. > Yes, but this happens only after the buffer is removed from wbuf[] as > I explain above. > > > Then, fsx-linux truncates the last a couple of buffers of a page. > > Then, block_write_full_page calls invalidatepage to invalidate the last a couple > > of buffers of the page, so the journal_heads of the buffer_head are unlinked and > > are marked as unmapped. > > Then, fsx-linux extend the file and does a msync after changing the page content > > by mmaping the page, so the page (inclduing the last buffer head) is marked dirty > > again. > > Then, kjournald's journal_commit_transaction goes through wbuf to submit_bh all > > dirty buffers, but one buffer head is already marked as unmapped. A bug check is > > triggerred. I think the reason that your patch fixes it is that journal_invalidatepage will lock the buffer before calling journal_unmap_buffer. So the last step to trigger the bug will be synced with journal_commit_transaction. > I think the right way is to let journal_dirty_data to wait till wbuf is flushed. > This actually happens in my fix too. And my fix has also a bonus of > fixing a few other flaws... Otherwise your patch seems to be right. Other flaws could be fixed by other small patches to make it clearer.