linux-kernel - Re: [PATCH v4] kcov, usb: only collect coverage from __usb_hcd_giveback

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Date:   Fri, 13 Nov 2020 16:32:53 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Shuah Khan <shuah@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Aleksandr Nogikh <nogikh@...gle.com>,
        Nazime Hande Harputluoglu <handeharput@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v4] kcov, usb: only collect coverage from
 __usb_hcd_giveback_urb in softirq

On Fri, Nov 13, 2020 at 02:42:44PM +0100, Andrey Konovalov wrote:
> On Fri, Nov 13, 2020 at 2:28 PM Sebastian Andrzej Siewior
> <bigeasy@...utronix.de> 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@mail.gmail.com/
> >
> > 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@linutronix.de
> >
> > 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?

I really have no idea, sorry.