Btrfs: remove root_log_ctx from ctx list before btrfs_sync_log returns

We use a btrfs_log_ctx structure to pass information into the
tree log commit, and get error values out.  It gets added to a per
log-transaction list which we walk when things go bad.

Commit d1433deb added an optimization to skip waiting for the log
commit, but didn't take root_log_ctx out of the list.  This
patch makes sure we remove things before exiting.
Signed-off-by: Chris Mason <clm@fb.com>
Fixes: d1433deb
cc: stable@vger.kernel.org # 3.15+

fs/btrfs/tree-log.c

@@ -2867,6 +2867,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 
 	if (log_root_tree->log_transid_committed >= root_log_ctx.log_transid) {
 		blk_finish_plug(&plug);
+		list_del_init(&root_log_ctx.list);
 		mutex_unlock(&log_root_tree->log_mutex);
 		ret = root_log_ctx.log_ret;
 		goto out;