From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932309AbdGJN4l (ORCPT ); Mon, 10 Jul 2017 09:56:41 -0400 Received: from mx2.suse.de ([195.135.220.15]:52063 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932108AbdGJN4k (ORCPT ); Mon, 10 Jul 2017 09:56:40 -0400 Subject: Re: [PATCH] btrfs: resume qgroup rescan on rw remount From: Nikolay Borisov To: Aleksa Sarai , Chris Mason , Josef Bacik , David Sterba Cc: linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Jeff Mahoney References: <20170704114906.8419-1-asarai@suse.de> <725eb058-4fb4-a167-9ba4-a062de718555@suse.com> Message-ID: <532a6e98-1745-4181-260a-38f4d5015857@suse.com> Date: Mon, 10 Jul 2017 16:56:36 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <725eb058-4fb4-a167-9ba4-a062de718555@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10.07.2017 16:12, Nikolay Borisov wrote: > > > On 4.07.2017 14:49, Aleksa Sarai wrote: >> Several distributions mount the "proper root" as ro during initrd and >> then remount it as rw before pivot_root(2). Thus, if a rescan had been >> aborted by a previous shutdown, the rescan would never be resumed. >> >> This issue would manifest itself as several btrfs ioctl(2)s causing the >> entire machine to hang when btrfs_qgroup_wait_for_completion was hit >> (due to the fs_info->qgroup_rescan_running flag being set but the rescan >> itself not being resumed). Notably, Docker's btrfs storage driver makes >> regular use of BTRFS_QUOTA_CTL_DISABLE and BTRFS_IOC_QUOTA_RESCAN_WAIT >> (causing this problem to be manifested on boot for some machines). >> >> Cc: # v3.11+ >> Cc: Jeff Mahoney >> Fixes: b382a324b60f ("Btrfs: fix qgroup rescan resume on mount") >> Signed-off-by: Aleksa Sarai > > Indeed, looking at the code it seems that b382a324b60f ("Btrfs: fix > qgroup rescan resume on mount") missed adding the qgroup_rescan_resume > in the remount path. One thing which I couldn't verify though is whether > reading fs_info->qgroup_flags without any locking is safe from remount > context. > > During remount I don't see any locks taken that prevent operations which > can modify qgroup_flags. > > Further inspection reveals that the access rules to qgroup_flags are somewhat broken so this patch doesn't really make things any worse than they are. As such: Reviewed-by: Nikolay Borisov Tested-by: Nikolay Borisov > >> --- >> fs/btrfs/super.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c >> index 6346876c97ea..ff6690389343 100644 >> --- a/fs/btrfs/super.c >> +++ b/fs/btrfs/super.c >> @@ -1821,6 +1821,8 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data) >> goto restore; >> } >> >> + btrfs_qgroup_rescan_resume(fs_info); >> + >> if (!fs_info->uuid_root) { >> btrfs_info(fs_info, "creating UUID tree"); >> ret = btrfs_create_uuid_tree(fs_info); >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >