Re: [PATCH] kcov: properly check if we are in an interrupt

[Vegard Nossum]

On 09/27/2016 09:50 AM, Dmitry Vyukov wrote:
> On Tue, Sep 27, 2016 at 9:34 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Tue, Sep 27, 2016 at 08:21:32AM +0200, Dmitry Vyukov wrote:
> > > I suspect there is a bunch of places that use in_interrupt(), but mean
> > > the same as KCOV wants -- am I in interrupt? and not am I in interrupt
> > > context or in normal task context but inside local_bh_disable(). For
> > > example, why does fput handles closure asynchronously if the task
> > > called local_bh_disable?
> >
> > Agreed, but it would mean auditing all in_interrupt()/irq_count() users.
>
>
> I don't think this means auditing all users. We are not making things
> worse by introduction of a new predicate.
> It would be nice to look at some uses in core code, but the only place
> with observed harm is KCOV.
>
> Any naming suggestions? Other than really_in_interrupt or
> in_interrupt_and_not_in_bh_disabled?

Your patch was:

-	if (!t || in_interrupt())
+	if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
+							| NMI_MASK)))

But look at the definitions:

#define irq_count()     (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \
                                 | NMI_MASK))
#define in_interrupt()          (irq_count())

So isn't the patch a no-op to start with?


Vegard