Hello.
Amit S. Kale wrote:
>>>>>>Even with this patch, the packets probably get stuck somewhere in the
>>>>>>driver, as cross-gdb sees tail of the $g packet reply only in reply to
>>>>>>next packet...
>> This wasn;t happeing on x86 probably because the register packet should
>>be much shorted there than on PPC...
>>>>> Argh! That's all because of the CONFIG_NETPOLL_TRAP that
>>>>>CONFIG_KGDBOE* options select -- since the initial breakpoint enables
>>>>>trapping via KGDBoE's pre_exception() handler, netif_{stop/wake}_queue()
>>>>>stop to work and that causes KGDBoE to literally flood 8139too with
>>>>>packets (although it can't queue up more than 4). Looks like a general
>>>>>design issue to me... :-/
>>>> Well, maybe not. But many drivers are surely unprepared to their
>>>>hard_start_xmit() method being called with queue alraedy stopped and
>>>>those with small TX queue (like natsemi with which we're also having
>>>>trouble) would get flooded as well. I'm going to submit a patch to
>>>>netdev adding extra check for TX ring being full -- after/if it gets
>>>>accepted, this patch won't be needed anymore.
>>>Here is what comes to my mind right away. It might need some more
>>>polishing or cleaning up:
>>>A potential solution will be to check the if hard_start_xmit() returns
>>>NETDEV_TX_BUSY. In case transmit queue is busy (due to lot of threads or
>>>queue getting full), we should wait in netpoll_send_skb(), call a cleanup
>>>through poll() and then retry sending packet.
>> This is already being done by netpoll iself. The thing is that
>>hard_start_xmit() doesdn't return NETDEV_TX_BUSY in those drivers. :-/
> In addition to that we set trapped. I wonder whether it is possible that a
> queue is stopped and we enter kgdb. It would be a deadlock.
> -Amit
Why? Netpoll does call the driver's interrupt and NAPI handlers in that
case (until the retry count is 0).
>>>Regards,
>>>Mithlesh Thukral
WBR, Sergei
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