[OpenWrt-Devel] OpenWrt cfg80211.h station_info incompatibility with kernel+mac80211 [was: B.A.T.M.A.N. V leaves the nest v2]

Sven Eckelmann sven at open-mesh.com
Thu Jan 21 08:47:30 EST 2016

On Thursday 21 January 2016 12:56:01 Sven Eckelmann wrote:
> Just installed in on some hardware (2x OM5P + OpenWrt 44654 + compat-wireless
> 2015-10-26) and enabled BATMAN_V.
> [  168.540000] CPU 0 Unable to handle kernel paging request at virtual address fffffff0, epc == 86d8301c, ra == 86d8301c
> [  168.550000] Oops[#1]:
> [  168.550000] CPU: 0 PID: 265 Comm: kworker/u2:2 Tainted: P               3.18.8 #1
> [  168.550000] Workqueue: bat_events batadv_v_elp_throughput_metric_update [batman_adv]
> [  168.550000] epc   : 86d8301c batadv_v_elp_throughput_metric_update+0x20/0x58 [batman_adv]
> [  168.550000]     Tainted: P              
> [  168.550000] ra    : 86d8301c batadv_v_elp_throughput_metric_update+0x20/0x58 [batman_adv]

Who knew that struct station_info changed in v3.18-6219-g6de3980,
v3.18-6235-gb51f3be and v3.18-6217-ga76b194? Wieder keiner!? :)

So what basically happened was a stack corruption causing the return address
to be bogus. This only happened because the kernel version of cfg80211.h (which
is used to compile batman-adv) is different than the version in the mac80211
package (which is used at runtime) I have now synced that structure between the
OpenWrt kernel and the used compat-wireless, rebuild my OpenWrt and tried again.
I hope this helps anyone trying to use B.A.T.M.A.N. V on OpenWrt.

@Felix, would it be ok for you when I propose a
"*-sync-cfg80211-station_info.patch" for the 3.18 generic kernel patches?
Or do you have a good idea how to force the openwrt-routing batman-adv package
against the cfg80211.h of compat-wireless?

Kind regards,
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