linux-kernel - [PATCH 3.16 034/133] btrfs: resume qgroup rescan on rw remount

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Message-ID: <lsq.1511315892.433609430@decadent.org.uk>
Date:   Wed, 22 Nov 2017 01:58:12 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "David Sterba" <dsterba@...e.com>,
        "Nikolay Borisov" <nborisov@...e.com>,
        "Jeff Mahoney" <jeffm@...e.com>, "Aleksa Sarai" <asarai@...e.de>
Subject: [PATCH 3.16 034/133] btrfs: resume qgroup rescan on rw remount

3.16.51-rc1 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>
[bwh: Backported to 3.16: add #include "qgroup.h"]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -59,6 +59,7 @@
 #include "free-space-cache.h"
 #include "backref.h"
 #include "tests/btrfs-tests.h"
+#include "qgroup.h"

 #define CREATE_TRACE_POINTS
 #include <trace/events/btrfs.h>
@@ -1495,6 +1496,8 @@ 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);