Re: [PATCH v4] kcov, usb: only collect coverage from __usb_hcd_giveback_urb in softirq

[Andrey Konovalov]

On Fri, Nov 13, 2020 at 2:28 PM Sebastian Andrzej Siewior
<bigeasy@xxxxxxxxxxxxx> wrote:
>
> On 2020-11-13 13:51:19 [+0100], Andrey Konovalov wrote:
> > Hi Sebastian,
>
> Hi Andrey,
>
> > Replaced with what and why?
>
> Linus requested in
>         https://lkml.kernel.org/r/CAHk-=wht7kAeyR5xEW2ORj7m0hibVxZ3t+2ie8vNHLQfdbN2_g@xxxxxxxxxxxxxx/
>
> that drivers should not change their behaviour on context magic like
> in_atomic(), in_interrupt() and so on.
> The USB bits were posted in
>         https://lkml.kernel.org/r/20201019100629.419020859@xxxxxxxxxxxxx
>
> and merged (which is probably the same time as this patch).
>
> I haven't look what this code should do or does but there are HCDs for
> which this is never true like the UHCI/OHCI controller for instance.

We could go back to adding softirq-specific kcov callbacks. Perhaps
with a simpler implementation than what we had before to only cover
this case. Something like kcov_remote_start_usb_softirq() and
kcov_remote_stop_softirq() that do the softirq check internally.

Greg, what would you prefer?