Patch "Btrfs: fix qgroup rescan worker initialization" has been added to the 4.9-stable tree

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

Btrfs: fix qgroup rescan worker initialization

to the 4.9-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-fix-qgroup-rescan-worker-initialization.patch
and it can be found in the queue-4.9 subdirectory.

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

From: Filipe Manana <[email protected]>
Date: Thu, 24 Nov 2016 02:09:04 +0000
Subject: Btrfs: fix qgroup rescan worker initialization

From: Filipe Manana <[email protected]>

commit 8d9eddad19467b008e0c881bc3133d7da94b7ec1 upstream.

We were setting the qgroup_rescan_running flag to true only after the rescan worker started (which is a task run by a queue). So if a user space task starts a rescan and immediately after asks to wait for the rescan worker to finish, this second call might happen before the rescan worker task starts running, in which case the rescan wait ioctl returns immediatley, not waiting for the rescan worker to finish.

This was making the fstest btrfs/022 fail very often.

---
 fs/btrfs/qgroup.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

@@ -2335,10 +2335,6 @@ static void btrfs_qgroup_rescan_worker(s
 	int err = -ENOMEM;
 	int ret = 0;
 
-	mutex_lock(&fs_info->qgroup_rescan_lock);
-	fs_info->qgroup_rescan_running = true;
-	mutex_unlock(&fs_info->qgroup_rescan_lock);
-
 	path = btrfs_alloc_path();
 	if (!path)
 		goto out;

@@ -2449,6 +2445,7 @@ qgroup_rescan_init(struct btrfs_fs_info
 		sizeof(fs_info->qgroup_rescan_progress));
 	fs_info->qgroup_rescan_progress.objectid = progress_objectid;
 	init_completion(&fs_info->qgroup_rescan_completion);
+	fs_info->qgroup_rescan_running = true;
 
 	spin_unlock(&fs_info->qgroup_lock);
 	mutex_unlock(&fs_info->qgroup_rescan_lock);

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

queue-4.9/btrfs-fix-qgroup-rescan-worker-initialization.patch queue-4.9/btrfs-fix-relocation-incorrectly-dropping-data-references.patch queue-4.9/btrfs-fix-deadlock-caused-by-fsync-when-logging-directory-entries.patch queue-4.9/btrfs-fix-emptiness-check-for-dirtied-extent-buffers-at-check_leaf.patch queue-4.9/btrfs-fix-tree-search-logic-when-replaying-directory-entry-deletes.patch queue-4.9/btrfs-fix-bug_on-in-btrfs_mark_buffer_dirty.patch