pnfs: Fix a problem where we gratuitously start doing I/O through the MDS

If the client has to stop in pnfs_update_layout() to wait for another
layoutget to complete, it currently exits and defaults to I/O through
the MDS if the layoutget was successful.

Fixes: d03360aa ("pNFS: Ensure we return the error if someone kills...")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: stable@vger.kernel.org # v4.20+

fs/nfs/pnfs.c

@@ -1890,7 +1890,7 @@ pnfs_update_layout(struct inode *ino,
 		spin_unlock(&ino->i_lock);
 		lseg = ERR_PTR(wait_var_event_killable(&lo->plh_outstanding,
 					!atomic_read(&lo->plh_outstanding)));
-		if (IS_ERR(lseg) || !list_empty(&lo->plh_segs))
+		if (IS_ERR(lseg))
 			goto out_put_layout_hdr;
 		pnfs_put_layout_hdr(lo);
 		goto lookup_again;