Re: CVS commit: src/sys/net

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

On Mon, Feb 15, 2016 at 6:35 PM, Roy Marples <roy%marples.name@localhost> wrote:
> On 15/02/2016 08:08, Ryota Ozaki wrote:
>> Module Name:  src
>> Committed By: ozaki-r
>> Date:         Mon Feb 15 08:08:04 UTC 2016
>>
>> Modified Files:
>>       src/sys/net: if.c if.h
>>
>> Log Message:
>> Run if_link_state_change in softint
>>
>> if_link_state_change can execute the network stack that is expected to
>> not run in hardware interrupt (at least now), however network drivers
>> may call it in hardware interrupt. Avoid that by introducing a new
>> softint for if_link_state_change.
>
> I don't know anything about softints, so this could be a silly question,
> but this change looks racey to me. Is there a guarantee anywhere that
> if_link_state_change() won't be called again before
> if_link_state_change_si() has been called?

Not guaranteed. Hmm, you're right. There is a race condition;
ifp->if_link_state can be overwritten before calling
if_link_state_change_si and it does matter if ifp->if_link_state
has been back to ifp->if_old_link_state. (If ifp->if_link_state
is different from ifp->if_old_link_state, it doesn't matter
because it's just that the later state wins.)

I think we can fix by returning from if_link_state_change_si
if ifp->if_link_state == ifp->if_old_link_state. Is it correct?

Thanks,
  ozaki-r