northd: fix infinite loop in ovn_allocate_tnlid()

In case if all tunnel ids are exhausted, ovn_allocate_tnlid() function
iterates over tnlids indefinitely when *hint < min.  This is because
when tnlid reaches max, next tnlid is min and for-loop never reaches exit
condition for tnlid != *hint.

This patch sets a starting hint value to OVN_MIN_DP_KEY_LOCAL (1).

The downside of this change is that first allocated tnlid becomes 2.
This shouldn't be a problem.

Signed-off-by: Vladislav Odintsov <odivlad@gmail.com>

lib/ovn-util.c

@@ -689,11 +689,17 @@ next_tnlid(uint32_t tnlid, uint32_t min, uint32_t max)
     return tnlid + 1 <= max ? tnlid + 1 : min;
 }
 
+static uint32_t
+prev_tnlid(uint32_t tnlid, uint32_t min, uint32_t max)
+{
+    return tnlid - 1 <= min ? tnlid - 1 : max;
+}
+
 uint32_t
 ovn_allocate_tnlid(struct hmap *set, const char *name, uint32_t min,
                    uint32_t max, uint32_t *hint)
 {
-    for (uint32_t tnlid = next_tnlid(*hint, min, max); tnlid != *hint;
+    for (uint32_t tnlid = *hint; tnlid != prev_tnlid(*hint, min, max);
          tnlid = next_tnlid(tnlid, min, max)) {
         if (ovn_add_tnlid(set, tnlid)) {
             *hint = tnlid;

northd/northd.c

@@ -1009,7 +1009,7 @@ build_datapaths(struct ovsdb_idl_txn *ovnsb_txn,
     }
 
     /* Assign new tunnel ids where needed. */
-    uint32_t hint = 0;
+    uint32_t hint = OVN_MIN_DP_KEY_LOCAL;
     LIST_FOR_EACH_SAFE (od, list, &both) {
         ovn_datapath_allocate_key(sbrec_chassis_table,
                                   datapaths, &dp_tnlids, od, &hint);

tests/ovn-northd.at

@@ -2822,6 +2822,32 @@ AT_CHECK([test $lsp02 = 3 && test $ls1 = 123])
 AT_CLEANUP
 ])
 
+OVN_FOR_EACH_NORTHD_NO_HV([
+AT_SETUP([check tunnel ids exhaustion])
+ovn_start
+
+# Create a fake chassis with vxlan encap to lower MAX DP tunnel key to 2^12
+ovn-sbctl \
+    --id=@e create encap chassis_name=hv1 ip="192.168.0.1" type="vxlan" \
+    -- --id=@c create chassis name=hv1 encaps=@e
+
+cmd="ovn-nbctl --wait=sb"
+
+for i in {1..4097..1}; do
+    cmd="${cmd} -- ls-add lsw-${i}"
+done
+
+eval $cmd
+
+check_row_count nb:Logical_Switch 4097
+wait_row_count sb:Datapath_Binding 4095
+
+OVS_WAIT_UNTIL([grep "all datapath tunnel ids exhausted" northd/ovn-northd.log])
+
+AT_CLEANUP
+])
+
+
 OVN_FOR_EACH_NORTHD_NO_HV([
 AT_SETUP([Logical Flow Datapath Groups])
 ovn_start