Re: CM-ITC, pch_can/c_can_pci, sendto() returning ENOBUFS

[Jacob Kroon <jacob.kroon@gmail.com>]

Hi Vincent,

On 9/20/22 03:23, Vincent Mailhol wrote:
> On Tue. 20 Sep. 2022 at 08:43, Jacob Kroon <jacob.kroon@gmail.com> wrote:
>> Hi Marc and Dario,
>>
>> On 9/16/22 06:14, Jacob Kroon wrote:
>> ...> What I do know is that if I revert commit:
>>>
>>> "can: c_can: cache frames to operate as a true FIFO"
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=387da6bc7a826cc6d532b1c0002b7c7513238d5f
>>>
>>> then everything looks good. I don't get any BUG messages, and the host
>>> has been running overnight without problems, so it seems to have fixed
>>> the network interface lockup as well.
>>
>> I ran the kernel *with* the commit above, and also with the following patch:
>>
>>> diff --git a/drivers/net/can/c_can/c_can_main.c b/drivers/net/can/c_can/c_can_main.c
>>> index 52671d1ea17d..4375dc70e21f 100644
>>> --- a/drivers/net/can/c_can/c_can_main.c
>>> +++ b/drivers/net/can/c_can/c_can_main.c
>>> @@ -1,3 +1,4 @@
>>> +#define DEBUG
>>>   /*
>>>    * CAN bus driver for Bosch C_CAN controller
>>>    *
>>> @@ -469,8 +470,15 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
>>>        if (c_can_get_tx_free(tx_ring) == 0)
>>>                netif_stop_queue(dev);
>>>
>>> -     if (idx < c_can_get_tx_tail(tx_ring))
>>> +     netdev_dbg(dev, "JAKR:%d:%d:%d:%d\n", idx,
>>> +                                           c_can_get_tx_head(tx_ring),
>>> +                                           c_can_get_tx_tail(tx_ring),
>>> +                                           c_can_get_tx_free(tx_ring));
>>> +
>>> +     if (idx < c_can_get_tx_tail(tx_ring)) {
>>>                cmd &= ~IF_COMM_TXRQST; /* Cache the message */
>>> +             netdev_dbg(dev, "JAKR:Caching messages\n");
>>> +     }
>>>
>>>        /* Store the message in the interface so we can call
>>>         * can_put_echo_skb(). We must do this before we enable
>>
>> and I've uploaded the entire log I could capture from /dev/kmsg, right
>> up to the hang, here:
>>
>> https://pastebin.com/6hvAcPc9
>>
>> What looks odd to me right from the start is that sometimes when idx
>> rolls over to 0, and *only* when it rolls over to 0, the CAN frame gets
>> cached because "idx < c_can_get_tx_tail(tx_ring)".
> 
> This looks like a classic integer wraparound issue. A cast to s32
> should do the trick:
>    (s32)idx - c_can_get_tx_tail(tx_ring) < 0
> 
> This is not tested. I let you double check. You can refer to this
> function for an example:
> https://elixir.bootlin.com/linux/v5.19/source/drivers/net/can/usb/etas_es58x/es58x_core.c#L336
> 

I tried that change but there is no change in behaviour, and I don't see 
why it would make a difference since both expressions "idx" and 
"c_can_get_tx_tail(tx_ring)" are unsigned expressions to begin with.

Regards,
Jacob