linux-kernel - [PATCH 4.4 26/31] btrfs: resume qgroup rescan on rw remount

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Message-Id: <20170912165248.703332895@linuxfoundation.org>
Date:   Tue, 12 Sep 2017 09:56:21 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jeff Mahoney <jeffm@...e.com>,
        Aleksa Sarai <asarai@...e.de>,
        Nikolay Borisov <nborisov@...e.com>,
        David Sterba <dsterba@...e.com>
Subject: [PATCH 4.4 26/31] btrfs: resume qgroup rescan on rw remount

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Aleksa Sarai <asarai@...e.de>

commit 6c6b5a39c4bf3dbd8cf629c9f5450e983c19dbb9 upstream.

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: Jeff Mahoney <jeffm@...e.com>
Fixes: b382a324b60f ("Btrfs: fix qgroup rescan resume on mount")
Signed-off-by: Aleksa Sarai <asarai@...e.de>
Reviewed-by: Nikolay Borisov <nborisov@...e.com>
Tested-by: Nikolay Borisov <nborisov@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/btrfs/super.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1727,6 +1727,8 @@ static int btrfs_remount(struct super_bl
 			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);