btrfs: remove BTRFS_FS_QUOTA_DISABLING flag

Currently, "btrfs quota enable" would fail after "btrfs quota disable" on
the first time with syslog output "qgroup_rescan_init failed with -22", but
it would succeed on the second time.

When "quota disable" is called, BTRFS_FS_QUOTA_DISABLING flag bit will be
set in fs_info->flags in btrfs_quota_disable(), but it will not be droppd
in btrfs_run_qgroups() (which is called in btrfs_commit_transaction())
because quota_root has already been freed. If "quota enable" is called
after that, both BTRFS_FS_QUOTA_DISABLING and BTRFS_FS_QUOTA_ENABLED flag
would be dropped in the btrfs_run_qgroups() since quota_root is not NULL.
This leads to the failure of "quota enable" on the first time.

BTRFS_FS_QUOTA_DISABLING flag is not used outside of "quota disable"
context and is equivalent to whether quota_root is NULL or not.
btrfs_run_qgroups() checks whether quota_root is NULL or not in the first
place.

So, let's remove BTRFS_FS_QUOTA_DISABLING flag.

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -708,7 +708,6 @@ struct btrfs_delayed_root;
 #define BTRFS_FS_OPEN				5
 #define BTRFS_FS_QUOTA_ENABLED			6
 #define BTRFS_FS_QUOTA_ENABLING			7
-#define BTRFS_FS_QUOTA_DISABLING		8
 #define BTRFS_FS_UPDATE_UUID_TREE_GEN		9
 #define BTRFS_FS_CREATING_FREE_SPACE_TREE	10
 #define BTRFS_FS_BTREE_ERR			11

fs/btrfs/qgroup.c

@@ -807,7 +807,6 @@ static int btrfs_clean_quota_tree(struct btrfs_trans_handle *trans,
 	}
 	ret = 0;
 out:
-	set_bit(BTRFS_FS_QUOTA_DISABLING, &root->fs_info->flags);
 	btrfs_free_path(path);
 	return ret;
 }
@@ -953,7 +952,6 @@ int btrfs_quota_disable(struct btrfs_trans_handle *trans,
 	if (!fs_info->quota_root)
 		goto out;
 	clear_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags);
-	set_bit(BTRFS_FS_QUOTA_DISABLING, &fs_info->flags);
 	btrfs_qgroup_wait_for_completion(fs_info, false);
 	spin_lock(&fs_info->qgroup_lock);
 	quota_root = fs_info->quota_root;
@@ -2086,8 +2084,6 @@ int btrfs_run_qgroups(struct btrfs_trans_handle *trans,
 
 	if (test_and_clear_bit(BTRFS_FS_QUOTA_ENABLING, &fs_info->flags))
 		set_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags);
-	if (test_and_clear_bit(BTRFS_FS_QUOTA_DISABLING, &fs_info->flags))
-		clear_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags);
 
 	spin_lock(&fs_info->qgroup_lock);
 	while (!list_empty(&fs_info->dirty_qgroups)) {