* stmmac: Race in coalesce timer and NAPI
@ 2018-09-21 9:19 Jose Abreu
2018-09-21 13:54 ` Eric Dumazet
0 siblings, 1 reply; 2+ messages in thread
From: Jose Abreu @ 2018-09-21 9:19 UTC (permalink / raw)
To: netdev@vger•kernel.org, Joao Pinto
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.
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
^ permalink raw reply [flat|nested] 2+ messages in thread* Re: stmmac: Race in coalesce timer and NAPI
2018-09-21 9:19 stmmac: Race in coalesce timer and NAPI Jose Abreu
@ 2018-09-21 13:54 ` Eric Dumazet
0 siblings, 0 replies; 2+ messages in thread
From: Eric Dumazet @ 2018-09-21 13:54 UTC (permalink / raw)
To: Jose Abreu, netdev@vger•kernel.org, Joao Pinto
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
^ permalink raw reply [flat|nested] 2+ messages in thread
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