On 09/21/2018 02:19 AM, Jose Abreu wrote:
> Hello,
>
> I'm getting a race in stmmac coalesce timer and the
> napi_schedule() interrupt and I'm asking for advice. Currently,
> we are scheduling NAPI in coalesce timer but this leads to
> stmmac_tx_clean() deadlock because this function tries to acquire
> queue lock.
This is strange. Which lock are you talking about ?
The napi_schedule() stuff should be enough to protect your use case.
>
> I find that this is not expected because only one instance of
> NAPI should run at same time so I was wondering if it is possible
> that xmit() callback is causing the deadlock ?
>
> BTW, this is solved by:
> - Directly call stmmac_tx_clean() in timer function AND
> - Use netif_tx_trylock() in stmmac_tx_clean(). Then, if queue
> is already locked we re-arm coalesce timer or reschedule NAPI.
>
> This is easily reproducible in an ARM board with 8 core running
> at 100MHz each.
>
> Thanks and Best Regards,
> Jose Miguel Abreu
>
It looks to me stmmac_napi_poll() should not apply/consume any budget for TX
completion.
The budget for a NAPI poll shared by RX and TX is really only for the RX side.
netpoll will specificall call the poll() with budget==0 to only drain TX
