From: Mingming Cao Subject: Re: [PATCH] ext4 can fail badly when device stops accepting BIO_RW_BARRIER requests. Date: Thu, 07 Feb 2008 16:22:37 -0800 Message-ID: <1202430157.3840.14.camel@localhost.localdomain> References: <18346.24466.83745.944149@notabene.brown> <1202358321.6497.5.camel@norville.austin.ibm.com> Reply-To: cmm@us.ibm.com Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Neil Brown , sct@redhat.com, akpm@linux-foundation.org, adilger@clusterfs.com, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: Dave Kleikamp Return-path: Received: from e3.ny.us.ibm.com ([32.97.182.143]:48890 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761402AbYBHAWk (ORCPT ); Thu, 7 Feb 2008 19:22:40 -0500 In-Reply-To: <1202358321.6497.5.camel@norville.austin.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, 2008-02-06 at 22:25 -0600, Dave Kleikamp wrote: > Duplicating Neil Brown's jbd patch for jbd2. I guess this can go > through the ext4 queue rather than straight into -mm. > Checked-in. Thanks Shaggy and Neil. Mingming > Neil's text: > > Some devices - notably dm and md - can change their behaviour in > response to BIO_RW_BARRIER requests. They might start out accepting > such requests but on reconfiguration, they find out that they cannot > any more. > > ext3 (and other filesystems) deal with this by always testing if > BIO_RW_BARRIER requests fail with EOPNOTSUPP, and retrying the write > requests without the barrier (probably after waiting for any pending > writes to complete). > > However there is a bug in the handling for this for ext3. > > When ext3 (jbd actually) decides to submit a BIO_RW_BARRIER request, > it sets the buffer_ordered flag on the buffer head. > If the request completes successfully, the flag STAYS SET. > > Other code might then write the same buffer_head after the device has > been reconfigured to not accept barriers. This write will then fail, > but the "other code" is not ready to handle EOPNOTSUPP errors and the > error will be treated as fatal. > > This can be seen without having to reconfigure a device at exactly the > wrong time by putting: > > if (buffer_ordered(bh)) > printk("OH DEAR, and ordered buffer\n"); > > > in the while loop in "commit phase 5" of journal_commit_transaction. > > If it ever prints the "OH DEAR ..." message (as it does sometimes for > me), then that request could (in different circumstances) have failed > with EOPNOTSUPP, but that isn't tested for. > > My proposed fix is to clear the buffer_ordered flag after it has been > used, as in the following patch. > > Thanks, > NeilBrown > > Signed-off-by: Dave Kleikamp > > diff -Nurp linux-2.6.24-mm1/fs/jbd2/commit.c linux/fs/jbd2/commit.c > --- linux-2.6.24-mm1/fs/jbd2/commit.c 2008-02-04 09:08:44.000000000 -0600 > +++ linux/fs/jbd2/commit.c 2008-02-06 22:11:14.000000000 -0600 > @@ -148,6 +148,8 @@ static int journal_submit_commit_record( > barrier_done = 1; > } > ret = submit_bh(WRITE, bh); > + if (barrier_done) > + clear_buffer_ordered(bh); > > /* is it possible for another commit to fail at roughly > * the same time as this one? If so, we don't want to > @@ -166,7 +168,6 @@ static int journal_submit_commit_record( > spin_unlock(&journal->j_state_lock); > > /* And try again, without the barrier */ > - clear_buffer_ordered(bh); > set_buffer_uptodate(bh); > set_buffer_dirty(bh); > ret = submit_bh(WRITE, bh); > > > - > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html