On Thursday 22 February 2007 21:01, Sergei Shtylyov wrote:
> Hello.
>
> Mithlesh Thukral 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
>
> > Regards,
> > Mithlesh Thukral
>
> WBR, Sergei
>
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