NFSv4.1: Fix nfs4_callback_recallslot to work with dynamic slot allocation

Ensure that the NFSv4.1 CB_RECALL_SLOT callback updates the slot table
target max slotid safely.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/callback_proc.c

@@ -576,7 +576,7 @@ __be32 nfs4_callback_recallslot(struct cb_recallslotargs *args, void *dummy,
 	if (args->crsa_target_max_slots == fc_tbl->max_slots)
 		goto out;
 
-	fc_tbl->target_highest_slotid = args->crsa_target_max_slots;
+	nfs41_set_target_slotid(fc_tbl, args->crsa_target_max_slots);
 	nfs41_handle_recall_slot(cps->clp);
 out:
 	dprintk("%s: exit with status = %d\n", __func__, ntohl(status));

fs/nfs/nfs4_fs.h

@@ -260,6 +260,8 @@ extern int nfs4_proc_layoutcommit(struct nfs4_layoutcommit_data *data,
 
 extern struct nfs4_slot *nfs4_alloc_slots(struct nfs4_slot_table *table,
 		u32 max_slots, gfp_t gfp_flags);
+extern void nfs41_set_target_slotid(struct nfs4_slot_table *tbl,
+		u32 target_highest_slotid);
 
 static inline bool
 is_ds_only_client(struct nfs_client *clp)

fs/nfs/nfs4proc.c

@@ -498,6 +498,14 @@ static void nfs41_set_target_slotid_locked(struct nfs4_slot_table *tbl,
 	tbl->generation++;
 }
 
+void nfs41_set_target_slotid(struct nfs4_slot_table *tbl,
+		u32 target_highest_slotid)
+{
+	spin_lock(&tbl->slot_tbl_lock);
+	nfs41_set_target_slotid_locked(tbl, target_highest_slotid);
+	spin_unlock(&tbl->slot_tbl_lock);
+}
+
 static void nfs41_set_server_slotid_locked(struct nfs4_slot_table *tbl,
 		u32 highest_slotid)
 {