Re: [PATCH] usb: gadget: dummy_hcd: execute hrtimer callback in softirq context

[Alexander Potapenko <glider@google.com>]

On Mon, Jul 29, 2024 at 4:23 AM <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@gmail.com>
>
> Commit a7f3813e589f ("usb: gadget: dummy_hcd: Switch to hrtimer transfer
> scheduler") switched dummy_hcd to use hrtimer and made the timer's
> callback be executed in the hardirq context.
>
> With that change, __usb_hcd_giveback_urb now gets executed in the hardirq
> context, which causes problems for KCOV and KMSAN.
>
> One problem is that KCOV now is unable to collect coverage from
> the USB code that gets executed from the dummy_hcd's timer callback,
> as KCOV cannot collect coverage in the hardirq context.
>
> Another problem is that the dummy_hcd hrtimer might get triggered in the
> middle of a softirq with KCOV remote coverage collection enabled, and that
> causes a WARNING in KCOV, as reported by syzbot. (I sent a separate patch
> to shut down this WARNING, but that doesn't fix the other two issues.)
>
> Finally, KMSAN appears to ignore tracking memory copying operations
> that happen in the hardirq context, which causes false positive
> kernel-infoleaks, as reported by syzbot.

Hi Andrey,

FWIW this problem is tracked as
https://github.com/google/kmsan/issues/92, I'll try to revisit it in
September.