Re: skbuff panic

[Oliver Hartkopp <socketcan@hartkopp.net>]

Answering myself:

I tested the latest 3.16.0-rc3-00149-g034a0f6 with tst-packet.c and it works
like charm. Receiving and sending with tst-packet is no problem.
I was using the SJA1000 based EMS PCMCIA card in my laptop for this test.

So I really wonder why (obviously) a CAN frame is processed by the PF_PACKET
reception handler at the start of your system?!?

Regards,
Oliver

On 06.07.2014 14:12, Oliver Hartkopp wrote:
> On 06.07.2014 07:07, Austin Schuh wrote:
> 
>> What makes you think that someone opened a PF_PACKET socket?  I'm
>> curious, since that observation may help me produce a more reliable
>> test case and debug it some more myself.
> 
> If you look in your call trace is says:
> 
> skb_push+0x38/0x39          (-->> which panics)
> packet_rcv_spkt+0x98/0xdf
> __netif_receive_skb_core+0x459/0x4dc
> get_parent_ip+0xe/0x3e
> __netif_receive_skb+0x53/0x65
> 
> As packet_rcv_spkt() is located in net/packet/af_packet.c there must be some
> user at this early stage of system boot to make PF_PACKET process the CAN frame.
> 
> In https://gitorious.org/linux-can/can-tests there's a tst-packet.c program
> which uses the PF_PACKET socket to send/receive CAN frames.
> 
> I was using tst-packet.c about four years ago for a test - without any
> problems. But maybe something in the network layer changed, so that CAN frame
> skbs need to be created with a different setup now.
> 
> I'll try ASAP if tst-packet.c still works as expected on my machine.
> 
>>
>> I'm going to work on reproducing the panic more reliable, and then
>> I'll give your patch a whirl.  Currently, only PCs that are on the
>> other end of cell modems out in the field seem to be triggering the
>> panic.  I'm hesitant to do excessive experimentation on something that
>> takes a plane trip to fix.  That just means that this will take longer
>> to debug that I'd like...
> 
> Indeed this should not be the plan ...
> Let's save the world by saving carbon dioxide ;-)
> 
> Best regards,
> Oliver
> 
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