From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.fusionio.com ([66.114.96.31]:38002 "EHLO mx2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756732Ab2INPU4 (ORCPT ); Fri, 14 Sep 2012 11:20:56 -0400 Received: from mail1.int.fusionio.com (mail1.int.fusionio.com [10.101.1.21]) by mx2.fusionio.com with ESMTP id zwTuuHuoBXlTt0mk (version=TLSv1 cipher=AES128-SHA bits=128 verify=NO) for ; Fri, 14 Sep 2012 09:20:55 -0600 (MDT) From: Josef Bacik To: Subject: [PATCH] Btrfs: fix race with freeze and free space inodes Date: Fri, 14 Sep 2012 11:26:20 -0400 Message-ID: <1347636380-30185-1-git-send-email-jbacik@fusionio.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-btrfs-owner@vger.kernel.org List-ID: 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); -- 1.7.7.6