NFSv4: Don't use the zero stateid with layoutget

The NFSv4.1 protocol explicitly forbids us from using the zero stateid
together with layoutget, so when we see that nfs4_select_rw_stateid()
is unable to return a valid delegation, lock or open stateid, then
we should initiate recovery and retry.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs4state.c

@@ -1064,8 +1064,7 @@ int nfs4_select_rw_stateid(struct nfs4_state *state,
 		 * choose to use.
 		 */
 		goto out;
-	nfs4_copy_open_stateid(dst, state);
-	ret = 0;
+	ret = nfs4_copy_open_stateid(dst, state) ? 0 : -EAGAIN;
 out:
 	if (nfs_server_capable(state->inode, NFS_CAP_STATEID_NFSV41))
 		dst->seqid = 0;

fs/nfs/pnfs.c

@@ -1915,6 +1915,7 @@ pnfs_update_layout(struct inode *ino,
 	 * stateid.
 	 */
 	if (test_bit(NFS_LAYOUT_INVALID_STID, &lo->plh_flags)) {
+		int status;
 
 		/*
 		 * The first layoutget for the file. Need to serialize per
@@ -1934,13 +1935,20 @@ pnfs_update_layout(struct inode *ino,
 		}
 
 		first = true;
-		if (nfs4_select_rw_stateid(ctx->state,
+		status = nfs4_select_rw_stateid(ctx->state,
 					iomode == IOMODE_RW ? FMODE_WRITE : FMODE_READ,
-					NULL, &stateid, NULL) != 0) {
+					NULL, &stateid, NULL);
+		if (status != 0) {
 			trace_pnfs_update_layout(ino, pos, count,
 					iomode, lo, lseg,
 					PNFS_UPDATE_LAYOUT_INVALID_OPEN);
-			goto out_unlock;
+			if (status != -EAGAIN)
+				goto out_unlock;
+			spin_unlock(&ino->i_lock);
+			nfs4_schedule_stateid_recovery(server, ctx->state);
+			pnfs_clear_first_layoutget(lo);
+			pnfs_put_layout_hdr(lo);
+			goto lookup_again;
 		}
 	} else {
 		nfs4_stateid_copy(&stateid, &lo->plh_stateid);