NFSv4.1: Deal effectively with interrupted RPC calls.

If an RPC call is interrupted, assume that the server hasn't processed
the RPC call so that the next time we use the slot, we know that if we
get a NFS4ERR_SEQ_MISORDERED or NFS4ERR_SEQ_FALSE_RETRY, we just have
to bump the sequence number.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4proc.c

@@ -420,17 +420,9 @@ static int nfs41_sequence_done(struct rpc_task *task, struct nfs4_sequence_res *
 	struct nfs4_session *session;
 	struct nfs4_slot *slot;
 	struct nfs_client *clp;
+	bool interrupted = false;
 	int ret = 1;
 
-	/*
-	 * sr_status remains 1 if an RPC level error occurred. The server
-	 * may or may not have processed the sequence operation..
-	 * Proceed as if the server received and processed the sequence
-	 * operation.
-	 */
-	if (res->sr_status == 1)
-		res->sr_status = NFS_OK;
-
 	/* don't increment the sequence number if the task wasn't sent */
 	if (!RPC_WAS_SENT(task))
 		goto out;
@@ -438,6 +430,11 @@ static int nfs41_sequence_done(struct rpc_task *task, struct nfs4_sequence_res *
 	slot = res->sr_slot;
 	session = slot->table->session;
 
+	if (slot->interrupted) {
+		slot->interrupted = 0;
+		interrupted = true;
+	}
+
 	/* Check the SEQUENCE operation status */
 	switch (res->sr_status) {
 	case 0:
@@ -450,6 +447,15 @@ static int nfs41_sequence_done(struct rpc_task *task, struct nfs4_sequence_res *
 			nfs4_schedule_lease_recovery(clp);
 		nfs41_update_target_slotid(slot->table, slot, res);
 		break;
+	case 1:
+		/*
+		 * sr_status remains 1 if an RPC level error occurred.
+		 * The server may or may not have processed the sequence
+		 * operation..
+		 * Mark the slot as having hosted an interrupted RPC call.
+		 */
+		slot->interrupted = 1;
+		goto out;
 	case -NFS4ERR_DELAY:
 		/* The server detected a resend of the RPC call and
 		 * returned NFS4ERR_DELAY as per Section 2.10.6.2
@@ -467,6 +473,14 @@ static int nfs41_sequence_done(struct rpc_task *task, struct nfs4_sequence_res *
 		 */
 		goto retry_nowait;
 	case -NFS4ERR_SEQ_MISORDERED:
+		/*
+		 * Was the last operation on this sequence interrupted?
+		 * If so, retry after bumping the sequence number.
+		 */
+		if (interrupted) {
+			++slot->seq_nr;
+			goto retry_nowait;
+		}
 		/*
 		 * Could this slot have been previously retired?
 		 * If so, then the server may be expecting seq_nr = 1!

fs/nfs/nfs4session.c

@@ -172,6 +172,7 @@ static void nfs4_reset_slot_table(struct nfs4_slot_table *tbl,
 	p = &tbl->slots;
 	while (*p) {
 		(*p)->seq_nr = ivalue;
+		(*p)->interrupted = 0;
 		p = &(*p)->next;
 	}
 	tbl->highest_used_slotid = NFS4_NO_SLOT;

fs/nfs/nfs4session.h

@@ -21,6 +21,7 @@ struct nfs4_slot {
 	unsigned long		generation;
 	u32			slot_nr;
 	u32		 	seq_nr;
+	unsigned int		interrupted : 1;
 };
 
 /* Sessions */