Btrfs: wake up transaction waiters when aborting a transaction

I was getting lots of hung tasks and a NULL pointer dereference because we
are not cleaning up the transaction properly when it aborts.  First we need
to reset the running_transaction to NULL so we don't get a bad dereference
for any start_transaction callers after this.  Also we cannot rely on
waitqueue_active() since it's just a list_empty(), so just call wake_up()
directly since that will do the barrier for us and such.  Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>

fs/btrfs/disk-io.c

@@ -3589,15 +3589,12 @@ void btrfs_cleanup_one_transaction(struct btrfs_transaction *cur_trans,
 	/* FIXME: cleanup wait for commit */
 	cur_trans->in_commit = 1;
 	cur_trans->blocked = 1;
-	if (waitqueue_active(&root->fs_info->transaction_blocked_wait))
 	wake_up(&root->fs_info->transaction_blocked_wait);
 
 	cur_trans->blocked = 0;
-	if (waitqueue_active(&root->fs_info->transaction_wait))
 	wake_up(&root->fs_info->transaction_wait);
 
 	cur_trans->commit_done = 1;
-	if (waitqueue_active(&cur_trans->commit_wait))
 	wake_up(&cur_trans->commit_wait);
 
 	btrfs_destroy_pending_snapshots(cur_trans);

fs/btrfs/transaction.c

@@ -1221,6 +1221,10 @@ static void cleanup_transaction(struct btrfs_trans_handle *trans,
 
 	spin_lock(&root->fs_info->trans_lock);
 	list_del_init(&cur_trans->list);
+	if (cur_trans == root->fs_info->running_transaction) {
+		root->fs_info->running_transaction = NULL;
+		root->fs_info->trans_no_join = 0;
+	}
 	spin_unlock(&root->fs_info->trans_lock);
 
 	btrfs_cleanup_one_transaction(trans->transaction, root);