Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752552AbYLRXRW (ORCPT ); Thu, 18 Dec 2008 18:17:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752994AbYLRXRL (ORCPT ); Thu, 18 Dec 2008 18:17:11 -0500 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:53339 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752908AbYLRXRJ (ORCPT ); Thu, 18 Dec 2008 18:17:09 -0500 Date: Fri, 19 Dec 2008 00:17:07 +0100 From: Jan Kara To: Arthur Jones Cc: Andrew Morton , "sandeen@redhat.com" , "linux-ext4@vger.kernel.org" , "sct@redhat.com" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] ext3: wait on all pending commits in ext3_sync_fs Message-ID: <20081218231707.GB20092@atrey.karlin.mff.cuni.cz> References: <4908C951.2000309@redhat.com> <20081103184426.GA31894@ajones-laptop.nbttech.com> <20081103113318.35b0c266.akpm@linux-foundation.org> <20081103201428.GB30565@ajones-laptop.nbttech.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081103201428.GB30565@ajones-laptop.nbttech.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6400 Lines: 173 Hello, I'm sorry I'm replying late but I got time to react to this only now... > On Mon, Nov 03, 2008 at 11:33:18AM -0800, Andrew Morton wrote: > > [...] > > > --- a/fs/ext3/super.c > > > +++ b/fs/ext3/super.c > > > @@ -2392,7 +2392,13 @@ static int ext3_sync_fs(struct super_block *sb, int wait) > > > if (journal_start_commit(EXT3_SB(sb)->s_journal, &target)) { > > > if (wait) > > > log_wait_commit(EXT3_SB(sb)->s_journal, target); > > > - } > > > + } else if (wait) > > > + /* > > > + * We may have a commit in progress, clear it out > > > + * before we go on... > > > + */ > > > + ext3_force_commit(sb); > > > + > > > return 0; > > > } > > > > Can we do > > > > sb->s_dirt = 0; > > if (wait) > > ext3_force_commit(...); > > else > > journal_start_commit(...); > > I think this is what you had in mind: > > > diff --git a/fs/ext3/super.c b/fs/ext3/super.c > index 18eaa78..2b48b85 100644 > --- a/fs/ext3/super.c > +++ b/fs/ext3/super.c > @@ -2386,13 +2386,12 @@ static void ext3_write_super (struct super_block * sb) > > static int ext3_sync_fs(struct super_block *sb, int wait) > { > - tid_t target; > - > sb->s_dirt = 0; > - if (journal_start_commit(EXT3_SB(sb)->s_journal, &target)) { > - if (wait) > - log_wait_commit(EXT3_SB(sb)->s_journal, target); > - } > + if (wait) > + ext3_force_commit(sb); > + else > + journal_start_commit(EXT3_SB(sb)->s_journal, NULL); > + > return 0; > } > > I tried this and it too fixes the problem. FWIW I agree it > looks better... Well, shouldn't we rather fix what journal_start_commit() returns? The interface which returns 1 when a transaction is already committing or a transaction commit has just been started but 0 when we race with somebody staring the commit is fairly unusable. Moreover ext3_force_commit() will unnecessarily create new sync transaction and commit it if there's no transaction running which is quite expensive (even merging empty sync handle is not for free because of sync transaction batching). But this is minor problem since we probably don't care too much about sync() performance - BTW this is probably a cause for bug 12224, isn't it? BTW: ocfs2 would need fixing as well if done your way since it's sync_fs function has been copied over from ext3. To summarized I'd rather see a patch like below (untested) going in and your patch reverted... Opinions? I can cookup a JBD2 version of the patch in case we agree to go this way. Honza >From 0a578ba1b56fe655570ee6dad41748863a120dbc Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Fri, 19 Dec 2008 00:05:34 +0100 Subject: [PATCH] jbd: Fix return value of journal_start_commit() journal_start_commit() returns 1 if either a transaction is committing or the function has queued a transaction commit. But it returns 0 if we raced with somebody queueing the transaction commit as well. This resulted in ext3_sync_fs() not functioning correctly (description from Arthur Jones): In the case of a data=ordered umount with pending long symlinks which are delayed due to a long list of other I/O on the backing block device, this causes the buffer associated with the long symlinks to not be moved to the inode dirty list in the second phase of fsync_super. Then, before they can be dirtied again, kjournald exits, seeing the UMOUNT flag and the dirty pages are never written to the backing block device, causing long symlink corruption and exposing new or previously freed block data to userspace. This can be reproduced with a script created by Eric Sandeen : #!/bin/bash umount /mnt/test2 mount /dev/sdb4 /mnt/test2 rm -f /mnt/test2/* dd if=/dev/zero of=/mnt/test2/bigfile bs=1M count=512 touch /mnt/test2/thisisveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylongfilename ln -s /mnt/test2/thisisveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylongfilename /mnt/test2/link umount /mnt/test2 mount /dev/sdb4 /mnt/test2 ls /mnt/test2/ This patch fixes journal_start_commit() to always return 1 when there's a transaction committing or queued for commit. Signed-off-by: Jan Kara --- fs/jbd/journal.c | 17 +++++++++++------ 1 files changed, 11 insertions(+), 6 deletions(-) diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c index 9e4fa52..e79c078 100644 --- a/fs/jbd/journal.c +++ b/fs/jbd/journal.c @@ -427,7 +427,7 @@ int __log_space_left(journal_t *journal) } /* - * Called under j_state_lock. Returns true if a transaction was started. + * Called under j_state_lock. Returns true if a transaction commit was started. */ int __log_start_commit(journal_t *journal, tid_t target) { @@ -495,7 +495,8 @@ int journal_force_commit_nested(journal_t *journal) /* * Start a commit of the current running transaction (if any). Returns true - * if a transaction was started, and fills its tid in at *ptid + * if a transaction is going to be committed (or is currently already + * committing), and fills its tid in at *ptid */ int journal_start_commit(journal_t *journal, tid_t *ptid) { @@ -505,15 +506,19 @@ int journal_start_commit(journal_t *journal, tid_t *ptid) if (journal->j_running_transaction) { tid_t tid = journal->j_running_transaction->t_tid; - ret = __log_start_commit(journal, tid); - if (ret && ptid) + __log_start_commit(journal, tid); + /* There's a running transaction and we've just made sure + * it's commit has been scheduled. */ + if (ptid) *ptid = tid; - } else if (journal->j_committing_transaction && ptid) { + ret = 1; + } else if (journal->j_committing_transaction) { /* * If ext3_write_super() recently started a commit, then we * have to wait for completion of that transaction */ - *ptid = journal->j_committing_transaction->t_tid; + if (ptid) + *ptid = journal->j_committing_transaction->t_tid; ret = 1; } spin_unlock(&journal->j_state_lock); -- 1.6.0.2 -- 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/