From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Monakhov Subject: Re: [PATCH 4/4] ext4: serialize truncate with owerwrite DIO workers Date: Wed, 05 Sep 2012 20:59:09 +0400 Message-ID: <87y5ko76ea.fsf@openvz.org> References: <1346780214-29845-1-git-send-email-dmonakhov@openvz.org> <1346780214-29845-4-git-send-email-dmonakhov@openvz.org> <20120905154920.GF18051@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org, jack@suse.cz To: Jan Kara Return-path: Received: from mail-lpp01m010-f46.google.com ([209.85.215.46]:44563 "EHLO mail-lpp01m010-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752001Ab2IEQ7N (ORCPT ); Wed, 5 Sep 2012 12:59:13 -0400 Received: by lagy9 with SMTP id y9so475811lag.19 for ; Wed, 05 Sep 2012 09:59:11 -0700 (PDT) In-Reply-To: <20120905154920.GF18051@quack.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, 5 Sep 2012 17:49:20 +0200, Jan Kara wrote: > On Tue 04-09-12 21:36:54, Dmitry Monakhov wrote: > > Jan Kara have spotted interesting issue: > > There are potential data corruption issue with direct IO overwrites > > racing with truncate: > > Like: > > dio write truncate_task > > ->ext4_ext_direct_IO > > ->overwrite == 1 > > ->down_read(&EXT4_I(inode)->i_data_sem); > > ->mutex_unlock(&inode->i_mutex); > > ->ext4_setattr() > > ->inode_dio_wait() > > ->truncate_setsize() > > ->ext4_truncate() > > ->down_write(&EXT4_I(inode)->i_data_sem); > > ->__blockdev_direct_IO > > ->ext4_get_block > > ->submit_io() > > ->up_read(&EXT4_I(inode)->i_data_sem); > > # truncate data blocks, allocate them to > > # other inode - bad stuff happens because > > # dio is still in flight. > > > > In order to serialize with truncate dio worker should grab extra i_dio_count > > reference before drop i_mutex. > Thanks for the patch. You can add: > Reviewed-by: Jan Kara I'm Sorry, but unfortunately in two line patch i've done one mistake :( because inode_dio_done() should be before i_mutex will be retaken otherwise following deadlock happen ext4_setattr ext4_direct_io mutex_unlock atomic_inc(inode->i_dio_count) mutex_lock(i_mutex) inode_dio_wait(inode) ->BLOCK DEADLOCK<- mutex_lock(i_mutex) inode_dio_done() So i'll add your review sing to updated version if you don't mind. > Honza > > Signed-off-by: Dmitry Monakhov > > --- > > fs/ext4/inode.c | 2 ++ > > 1 files changed, 2 insertions(+), 0 deletions(-) > > > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > > index 5a75908..9725acb 100644 > > --- a/fs/ext4/inode.c > > +++ b/fs/ext4/inode.c > > @@ -3035,6 +3035,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb, > > overwrite = *((int *)iocb->private); > > > > if (overwrite) { > > + atomic_inc(&inode->i_dio_count); > > down_read(&EXT4_I(inode)->i_data_sem); > > mutex_unlock(&inode->i_mutex); > > } > > @@ -3134,6 +3135,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb, > > if (overwrite) { > > up_read(&EXT4_I(inode)->i_data_sem); > > mutex_lock(&inode->i_mutex); > > + inode_dio_done(inode); > > } > > > > return ret; > > -- > > 1.7.7.6 > > > -- > Jan Kara > SUSE Labs, CR > -- > 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