NFS: Fix a memory leak in nfs_do_recoalesce

If the function exits early, then we must put those requests that were
not processed back onto the &mirror->pg_list so they can be cleaned up
by nfs_pgio_error().

Fixes: a7d42ddb30997 ("nfs: add mirroring support to pgio layer")
Cc: stable@vger.kernel.org # v4.0+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/pagelist.c

@@ -1109,8 +1109,11 @@ static int nfs_do_recoalesce(struct nfs_pageio_descriptor *desc)
 			nfs_list_remove_request(req);
 			if (__nfs_pageio_add_request(desc, req))
 				continue;
-			if (desc->pg_error < 0)
+			if (desc->pg_error < 0) {
+				list_splice_tail(&head, &mirror->pg_list);
+				mirror->pg_recoalesce = 1;
 				return 0;
+			}
 			break;
 		}
 	} while (mirror->pg_recoalesce);