NFS: Don't recoalesce on error in nfs_pageio_complete_mirror()

If the I/O completion failed with a fatal error, then we should just
exit nfs_pageio_complete_mirror() rather than try to recoalesce.

Fixes: a7d42ddb ("nfs: add mirroring support to pgio layer")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: stable@vger.kernel.org # v4.0+

fs/nfs/pagelist.c

@@ -1209,7 +1209,7 @@ static void nfs_pageio_complete_mirror(struct nfs_pageio_descriptor *desc,
 		desc->pg_mirror_idx = mirror_idx;
 	for (;;) {
 		nfs_pageio_doio(desc);
-		if (!mirror->pg_recoalesce)
+		if (desc->pg_error < 0 || !mirror->pg_recoalesce)
 			break;
 		if (!nfs_do_recoalesce(desc))
 			break;