> Il 01/03/2021 12:36 Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> ha scritto:
>
>
> 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.
Yes, you are right. I was misled by the name of the function.
>
> 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.
I agree with you, I'll do it.
Thanks and regards,
Dario
>
> regards,
> Marc
>
> --
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