From: Jan Kara Subject: Re: [PATCH] jbd: clear b_modified before moving the jh to a different transaction Date: Wed, 4 Apr 2012 09:55:20 +0200 Message-ID: <20120404075520.GA5725@quack.suse.cz> References: <1326219175-4529-1-git-send-email-josef@redhat.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="YZ5djTAD1cGYuMQK" Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, jack@suse.cz To: Josef Bacik Return-path: Received: from cantor2.suse.de ([195.135.220.15]:49718 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753088Ab2DDHzY (ORCPT ); Wed, 4 Apr 2012 03:55:24 -0400 Content-Disposition: inline In-Reply-To: <1326219175-4529-1-git-send-email-josef@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: --YZ5djTAD1cGYuMQK Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue 10-01-12 13:12:55, Josef Bacik wrote: > If we are journalling data (ie journal=data or big symlinks) we can discard > buffers and move them to different transactions to make sure they get cleaned up > properly. The problem is b_modified could still be set from the last > transaction that touched it, so putting it on the currently running transaction > or setting it up to be put on the next transaction will run into problems if the > buffer gets reused in that transaction as the space accounting logic won't be > done, which will result in panics at commit time because t_nr_buffers will end > up being more than t_outstanding_credits. Thanks to Jan Kara for pointing out > the other part of this problem a few months ago. Thanks, > > Signed-off-by: Josef Bacik So I think I've nailed this down. Your feeling that the problem is with refiling buffer to BJ_Forget list of the running transaction was right. The missing piece to the puzzle was that journal_invalidatepage() can get called not only when underlying block is freed but also when someone flushes page cache. The traces I have suggest that someone has flushed page cache (likely of the block device), that moved buffer from the checkpoint list to BJ_Forget list of the running transaction and then the same running transaction tried to modify the buffer which triggered the accounting problem you spotted. I have updated the changelog and pushed the patch to my tree (for JBD only). I'll duplicate the patch for JBD2 tomorrow. Honza -- Jan Kara SUSE Labs, CR --YZ5djTAD1cGYuMQK Content-Type: text/x-patch; charset=us-ascii Content-Disposition: attachment; filename="0001-jbd-clear-b_modified-before-moving-the-jh-to-a-diffe.patch" >From d433e0479c9cde46b29b30a5c5996c1dbe57005f Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Tue, 10 Jan 2012 13:12:55 -0500 Subject: [PATCH] jbd: clear b_modified before moving the jh to a different transaction journal_forget() and journal_invalidatepage() functions move buffer to BJ_Forget list of a running transaction so that the buffer gets cleaned up when the transaction is committed. This usually happens when underlying block is freed but journal_invalidatepage() can also move the buffer when page cache of the corresponding inode (may be a block device) gets flushed. When the buffer had b_modfied set from the previous transaction and we happen to modify it again in the current transaction, we won't properly account for the modified buffer by subtracting the number of reserved credits of the running transaction because do_get_write_access() won't clear b_modified (buffer already is on running transaction so do_get_write_access() things it has nothing to do). This then results in assertion failure in commit code because the transaction has more buffers than reserved credits (t_nr_buffers > t_outstanding_credits). We fix the issue by clearing b_modified before moving buffer to a BJ_Forget list of another transaction because logically, it's not changed for that transaction anymore. CC: stable@kernel.org Signed-off-by: Josef Bacik Signed-off-by: Jan Kara --- fs/jbd/transaction.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-) diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c index febc10d..fb48e44 100644 --- a/fs/jbd/transaction.c +++ b/fs/jbd/transaction.c @@ -1788,6 +1788,7 @@ static int __dispose_buffer(struct journal_head *jh, transaction_t *transaction) */ clear_buffer_dirty(bh); __journal_file_buffer(jh, transaction, BJ_Forget); + jh->b_modified = 0; may_free = 0; } else { JBUFFER_TRACE(jh, "on running transaction"); @@ -1956,8 +1957,10 @@ static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh) * clear dirty bits when it is done with the buffer. */ set_buffer_freed(bh); - if (journal->j_running_transaction && buffer_jbddirty(bh)) + if (journal->j_running_transaction && buffer_jbddirty(bh)) { + jh->b_modified = 0; jh->b_next_transaction = journal->j_running_transaction; + } journal_put_journal_head(jh); spin_unlock(&journal->j_list_lock); jbd_unlock_bh_state(bh); -- 1.7.1 --YZ5djTAD1cGYuMQK--