[PATCH] btrfs: resume qgroup rescan on rw remount

From	Aleksa Sarai <asarai@suse.de>
Newsgroups	linux.kernel
Subject	[PATCH] btrfs: resume qgroup rescan on rw remount
Date	2017-07-04 13:50 +0200
Message-ID	<tZuv7-7I0-5@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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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: <stable@vger.kernel.org> # v3.11+
Cc: Jeff Mahoney <jeffm@suse.com>
Fixes: b382a324b60f ("Btrfs: fix qgroup rescan resume on mount")
Signed-off-by: Aleksa Sarai <asarai@suse.de>
---
 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);
-- 
2.13.2

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[PATCH] btrfs: resume qgroup rescan on rw remount Aleksa Sarai <asarai@suse.de> - 2017-07-04 13:50 +0200
  Re: [PATCH] btrfs: resume qgroup rescan on rw remount Nikolay Borisov <nborisov@suse.com> - 2017-07-10 15:20 +0200
    Re: [PATCH] btrfs: resume qgroup rescan on rw remount Nikolay Borisov <nborisov@suse.com> - 2017-07-10 16:00 +0200
      Re: [PATCH] btrfs: resume qgroup rescan on rw remount David Sterba <dsterba@suse.cz> - 2017-07-11 19:10 +0200

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