NFSv4.1: Defer bumping the slot sequence number until we free the slot

For operations like OPEN or LAYOUTGET, which return recallable state
(i.e. delegations and layouts) we want to enable the mechanism for
resolving recall races in RFC5661 Section 2.10.6.3.
To do so, we will want to defer bumping the slot's sequence number until
we have finished processing the RPC results.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/nfs4proc.c

@@ -666,6 +666,11 @@ static void nfs41_sequence_free_slot(struct nfs4_sequence_res *res)
 	tbl = slot->table;
 	session = tbl->session;
 
+	/* Bump the slot sequence number */
+	if (slot->seq_done)
+		slot->seq_nr++;
+	slot->seq_done = 0;
+
 	spin_lock(&tbl->slot_tbl_lock);
 	/* Be nice to the server: try to ensure that the last transmitted
 	 * value for highest_user_slotid <= target_highest_slotid
@@ -716,7 +721,7 @@ int nfs41_sequence_done(struct rpc_task *task, struct nfs4_sequence_res *res)
 	switch (res->sr_status) {
 	case 0:
 		/* Update the slot's sequence and clientid lease timer */
-		++slot->seq_nr;
+		slot->seq_done = 1;
 		clp = session->clp;
 		do_renew_lease(clp, res->sr_timestamp);
 		/* Check sequence flags */
@@ -771,7 +776,7 @@ int nfs41_sequence_done(struct rpc_task *task, struct nfs4_sequence_res *res)
 		goto retry_nowait;
 	default:
 		/* Just update the slot sequence no. */
-		++slot->seq_nr;
+		slot->seq_done = 1;
 	}
 out:
 	/* The session may be reset by one of the error handlers. */

fs/nfs/nfs4session.h

@@ -21,7 +21,8 @@ struct nfs4_slot {
 	unsigned long		generation;
 	u32			slot_nr;
 	u32		 	seq_nr;
-	unsigned int		interrupted : 1;
+	unsigned int		interrupted : 1,
+				seq_done : 1;
 };
 
 /* Sessions */