Open-Mesh » batman-adv

Just in case somebody is interested: The first commit which has this problem during a bisect is b05bbab5e1fc ("batman-adv: B.A.T.M.A.N. V - implement neighbor comparison API calls"). But this commit is also the one which makes it possible to select BATMAN_V the first time (so the problem is most likely not hidden in this single commit).

There are still following commits:

b05bbab5e1fc ("batman-adv: B.A.T.M.A.N. V - implement neighbor comparison API calls")
bedcadfaa92b ("batman-adv: ELP - send unicast ELP packets for throughput sampling")
5c3245172c01 ("batman-adv: ELP - compute the metric based on the estimated throughput")
cdc4545350d1 ("batman-adv: keep track of when unicast packets are sent")
c513176e4b7a ("batman-adv: add throughput override attribute to hard_ifaces")
667996ebeab4 ("batman-adv: OGMv2 - implement originators logic")
632835348e65 ("batman-adv: OGMv2 - add basic infrastructure")
82da7d6cae2e ("batman-adv: ELP - adding sysfs parameter for elp interval")
2c2fe0ba9ea5 ("batman-adv: ELP - creating neighbor structures")
a4b88af77e28 ("batman-adv: ELP - adding basic infrastructure")
ec46535b8275 ("batman-adv: Add hard_iface specific sysfs wrapper macros for UINT")

The interesting part can be seen by modifying the elp code a little bit:

diff --git a/net/batman-adv/bat_v_elp.c b/net/batman-adv/bat_v_elp.c
index f257897..aeda5ba 100644
--- a/net/batman-adv/bat_v_elp.c
+++ b/net/batman-adv/bat_v_elp.c
@@ -254,8 +254,10 @@ static void batadv_v_elp_periodic_work(struct work_struct *work)
         goto out;

     /* the interface was enabled but may not be ready yet */
-    if (hard_iface->if_status != BATADV_IF_ACTIVE)
+    if (hard_iface->if_status != BATADV_IF_ACTIVE) {
+        printk("Restart timer %s:%u %u\n", __func__, __LINE__, hard_iface->if_status);
         goto restart_timer;
+    }

     skb = skb_copy(hard_iface->bat_v.elp_skb, GFP_ATOMIC);
     if (!skb)

You can see that it will spam periodically in the kernel log (2 BATADV_IF_INACTIVE, 4 BATADV_IF_TO_BE_ACTIVATED):

root@node01:~# /host/testme.sh 
batman_adv: B.A.T.M.A.N. advanced 2015.2-134-gb05bbab-dirty (compatibility version 15) loaded
batman_adv: bat0: Adding interface: dummy0
batman_adv: bat0: The MTU of interface dummy0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
batman_adv: bat0: Not using interface dummy0 (retrying later): interface not active
Restart timer batadv_v_elp_periodic_work:258 2
Restart timer batadv_v_elp_periodic_work:258 2
batman_adv: bat0: Interface activated: dummy0
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
Restart timer batadv_v_elp_periodic_work:258 4
unregister_netdevice: waiting for bat0 to become free. Usage count = 3

Message from syslogd@sven-edge at Mar 19 10:08:20 ...
 kernel:unregister_netdevice: waiting for bat0 to become free. Usage count = 3

The first commit introducing this code was a4b88af77e28 ("batman-adv: ELP - adding basic infrastructure"). But I haven't checked the code in detail. Especially not why it isn't marked as active via batadv_schedule_bat_ogm

I can see that batadv_hardif_disable_interface is called for this interface but it is not removed because it is not yet marked as "BATADV_IF_INACTIVE".

--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -571,12 +571,15 @@ void batadv_hardif_disable_interface(struct batadv_hard_iface *hard_iface,
 {
     struct batadv_priv *bat_priv = netdev_priv(hard_iface->soft_iface);
     struct batadv_hard_iface *primary_if = NULL;
+    printk("%s:%u\n", __func__, __LINE__);

     if (hard_iface->if_status == BATADV_IF_ACTIVE)
         batadv_hardif_deactivate_interface(hard_iface);
+    printk("%s:%u\n", __func__, __LINE__);

     if (hard_iface->if_status != BATADV_IF_INACTIVE)
         goto out;
+    printk("%s:%u\n", __func__, __LINE__);

     batadv_info(hard_iface->soft_iface, "Removing interface: %s\n",
             hard_iface->net_dev->name);

root@node01:~# /host/testme.sh 
batman_adv: B.A.T.M.A.N. advanced 2016.0-94-g77ddf97-dirty (compatibility version 15) loaded
batman_adv: bat0: Adding interface: dummy0
batman_adv: bat0: The MTU of interface dummy0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
batman_adv: bat0: Not using interface dummy0 (retrying later): interface not active
Restart timer batadv_v_elp_periodic_work:260 2
batman_adv: bat0: Interface activated: dummy0
batadv_hardif_disable_interface:574
batadv_hardif_disable_interface:578
unregister_netdevice: waiting for bat0 to become free. Usage count = 3

This works fine for BATMAN_IV

root@node01:~# /host/testme.sh 
batman_adv: B.A.T.M.A.N. advanced 2016.0-94-g77ddf97-dirty (compatibility version 15) loaded
batman_adv: bat0: Adding interface: dummy0
batman_adv: bat0: The MTU of interface dummy0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
batman_adv: bat0: Not using interface dummy0 (retrying later): interface not active
batman_adv: bat0: Interface activated: dummy0
batadv_hardif_disable_interface:574
batman_adv: bat0: Interface deactivated: dummy0
batadv_hardif_disable_interface:578
batadv_hardif_disable_interface:582
batman_adv: bat0: Removing interface: dummy0

But this is to be expected because the interface is marked as BATADV_IF_ACTIVE. And if this is really the problem then this can be worked around (please check this twice) via:

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index 3240a67..40e8e5a 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -572,7 +572,8 @@ void batadv_hardif_disable_interface(struct batadv_hard_iface *hard_iface,
     struct batadv_priv *bat_priv = netdev_priv(hard_iface->soft_iface);
     struct batadv_hard_iface *primary_if = NULL;

-    if (hard_iface->if_status == BATADV_IF_ACTIVE)
+    if (hard_iface->if_status == BATADV_IF_ACTIVE ||
+        hard_iface->if_status == BATADV_IF_TO_BE_ACTIVATED)
         batadv_hardif_deactivate_interface(hard_iface);

     if (hard_iface->if_status != BATADV_IF_INACTIVE)

Just had a look at the code and it looks like batadv_schedule_bat_ogm is called but the interface is still in mode INACTIVE.

BATMAN_IV does the same but calls it again later with the active interface:

batman_adv: bat0: Adding interface: dummy0
batman_adv: bat0: The MTU of interface dummy0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
batman_adv: bat0: Not using interface dummy0 (retrying later): interface not active
batadv_hardif_enable_interface:572
batadv_schedule_bat_ogm:434
batadv_schedule_bat_ogm:440 2
batman_adv: bat0: Interface activated: dummy0
batadv_schedule_bat_ogm:440 4
batadv_schedule_bat_ogm:440 3
batman_adv: bat0: Interface deactivated: dummy0
batman_adv: bat0: Removing interface: dummy0

"Problem" is here that BATMAN_V doesn't do anything with batadv_v_ogm_schedule. So it doesn't call batadv_schedule_bat_ogm again to active the interface. The interface will therefore forever in the TO_BE_ACTIVATED state and thus "inactive" for batman-adv.

BATMAN_IV instead uses bat_ogm_schedule to queue itself up for additional sends and thus later sets this interface to the state BATADV_IF_ACTIVE. This is done via batadv_send_outstanding_bat_ogm_packet for each batadv_forw_packet (see batadv_iv_ogm_aggregate_new).

The commit adding the problematic empty bat_ogm_schedule was a4b88af77e28 ("batman-adv: ELP - adding basic infrastructure")

The main topic of this issue has been addressed with the patch Sven proposed and I just merged into the next branch. What remains is that once a slave interface is turned off BATMAN V is never able to recover. That is largely due to the fact that BATMAN V does not take advantage of the general queuing mechanism (emit / schedule functions) but implements its own queue. Also missing is the batman_queue_left mechanism.

I can confirm that Antonio's patch fixes the issue.