From: Dave Kleikamp Subject: [PATCH] ext4 can fail badly when device stops accepting BIO_RW_BARRIER requests. Date: Wed, 06 Feb 2008 22:25:21 -0600 Message-ID: <1202358321.6497.5.camel@norville.austin.ibm.com> References: <18346.24466.83745.944149@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: sct@redhat.com, akpm@linux-foundation.org, adilger@clusterfs.com, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: Neil Brown Return-path: Received: from e2.ny.us.ibm.com ([32.97.182.142]:34789 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755307AbYBGEZ0 (ORCPT ); Wed, 6 Feb 2008 23:25:26 -0500 In-Reply-To: <18346.24466.83745.944149@notabene.brown> Sender: linux-ext4-owner@vger.kernel.org List-ID: Duplicating Neil Brown's jbd patch for jbd2. I guess this can go through the ext4 queue rather than straight into -mm. 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);