On 28.02.2021 11:35:31, Dario Binacchi wrote:
> > On 25.02.2021 22:51:52, Dario Binacchi wrote:
> > > According to commit 640916db2bf7 ("can: c_can: Make it SMP safe") let RX use
> > > IF1 (i.e. IF_RX) and TX use IF2 (i.e. IF_TX).
> >
> > Is this a fix?
> >
>
> I think that If I consider what is described in the 640916db2bf7
> commit, using the IF_RX interface in a tx routine is wrong.
Yes, IF_RX is used in c_can_do_tx(), but that's called from
c_can_poll(), which runs ins NAPI.
As far as I understand 640916db2bf7 ("can: c_can: Make it SMP safe")
fixes the race condition that c_can_poll() and c_can_start_xmit() both
access the same IF. See again the patch description:
| The hardware has two message control interfaces, but the code only uses the
| first one. So on SMP the following can be observed:
|
| CPU0 CPU1
| rx_poll()
| write IF1 xmit()
| write IF1
| write IF1
It's not 100% accurate, as the race condition is not just
c_can_do_rx_poll() against the c_can_start_xmit(), but the whole
c_can_poll() against c_can_start_xmit().
If you think my analysis is correct, please update the patch and add a
comment to clarify why IF_RX is used instead of changing it to IF_TX.
regards,
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
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