From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([222.73.24.84]:53872 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751170Ab2IQFhE (ORCPT ); Mon, 17 Sep 2012 01:37:04 -0400 Message-ID: <5056B6F9.4000708@cn.fujitsu.com> Date: Mon, 17 Sep 2012 13:36:57 +0800 From: Miao Xie Reply-To: miaox@cn.fujitsu.com MIME-Version: 1.0 To: Josef Bacik CC: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] Btrfs: fix race with freeze and free space inodes References: <1347636380-30185-1-git-send-email-jbacik@fusionio.com> In-Reply-To: <1347636380-30185-1-git-send-email-jbacik@fusionio.com> Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On fri, 14 Sep 2012 11:26:20 -0400, Josef Bacik wrote: > So we start our freeze, somebody comes in and does an fsync() on a file > where we have to commit a transaction for whatever reason, and we will > deadlock because the freeze is waiting on FS_FREEZE people to stop writing > to the file system, but the transaction is waiting for its free space inodes > to be written out, which are in turn waiting on sb_start_intwrite while > trying to write the file extents. To fix this we'll just skip the > sb_start_intwrite() if we TRANS_JOIN_NOLOCK since we're being waited on by a > transaction commit so we're safe wrt to freeze and this will keep us from > deadlocking. Thanks, > > Signed-off-by: Josef Bacik > --- > fs/btrfs/transaction.c | 10 +++++++++- > 1 files changed, 9 insertions(+), 1 deletions(-) > > diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c > index c9265a6..ba74dfb 100644 > --- a/fs/btrfs/transaction.c > +++ b/fs/btrfs/transaction.c > @@ -342,7 +342,15 @@ again: > if (!h) > return ERR_PTR(-ENOMEM); > > - if (!__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) { > + /* > + * If we are JOIN_NOLOCK we're already committing a transaction and > + * waiting on this guy, so we don't need to do the sb_start_intwrite > + * because we're already holding a ref. We need this because we could > + * have raced in and did an fsync() on a file which can kick a commit > + * and then we deadlock with somebody doing a freeze. > + */ > + if (type != TRANS_JOIN_NOLOCK && > + !__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) { > if (type == TRANS_JOIN_FREEZE) > return ERR_PTR(-EPERM); > sb_start_intwrite(root->fs_info->sb); > This patch forgets to deal with it in __btrfs_end_transaction(), or the freeze counter will be wrong. Thanks Miao