Patch "btrfs: resume qgroup rescan on rw remount" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

btrfs: resume qgroup rescan on rw remount

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-resume-qgroup-rescan-on-rw-remount.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Aleksa Sarai <[email protected]>
Date: Tue, 4 Jul 2017 21:49:06 +1000
Subject: btrfs: resume qgroup rescan on rw remount

From: Aleksa Sarai <[email protected]>

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).

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

@@ -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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/btrfs-resume-qgroup-rescan-on-rw-remount.patch