xfs: don't fail xfs_extent_busy allocation

commit 5e30c23d upstream.

We don't just need the structure to track busy extents which can be
avoided with a synchronous transaction, but also to keep track of
pending discard.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/xfs/xfs_extent_busy.c

@@ -45,18 +45,7 @@ xfs_extent_busy_insert(
 	struct rb_node		**rbp;
 	struct rb_node		*parent = NULL;
 
-	new = kmem_zalloc(sizeof(struct xfs_extent_busy), KM_MAYFAIL);
-	if (!new) {
-		/*
-		 * No Memory!  Since it is now not possible to track the free
-		 * block, make this a synchronous transaction to insure that
-		 * the block is not reused before this transaction commits.
-		 */
-		trace_xfs_extent_busy_enomem(tp->t_mountp, agno, bno, len);
-		xfs_trans_set_sync(tp);
-		return;
-	}
-
+	new = kmem_zalloc(sizeof(struct xfs_extent_busy), KM_SLEEP);
 	new->agno = agno;
 	new->bno = bno;
 	new->length = len;