NFSv4: Revert commit 5f83d86c ("NFSv4.x: Fix wraparound issues..")

commit fc40724f upstream.

The correct behaviour for NFSv4 sequence IDs is to wrap around
to the value 0 after 0xffffffff.
See https://tools.ietf.org/html/rfc5661#section-2.10.6.1

Fixes: 5f83d86c ("NFSv4.x: Fix wraparound issues when validing...")
Cc: stable@vger.kernel.org # 4.6+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/nfs/callback_proc.c

@@ -402,11 +402,8 @@ validate_seqid(const struct nfs4_slot_table *tbl, const struct nfs4_slot *slot,
 		return htonl(NFS4ERR_SEQ_FALSE_RETRY);
 	}
 
-	/* Wraparound */
-	if (unlikely(slot->seq_nr == 0xFFFFFFFFU)) {
-		if (args->csa_sequenceid == 1)
-			return htonl(NFS4_OK);
-	} else if (likely(args->csa_sequenceid == slot->seq_nr + 1))
+	/* Note: wraparound relies on seq_nr being of type u32 */
+	if (likely(args->csa_sequenceid == slot->seq_nr + 1))
 		return htonl(NFS4_OK);
 
 	/* Misordered request */