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

From: Vegard Nossum
Date: Tue Sep 27 2016 - 07:22:18 EST

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

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 \
#define in_interrupt() (irq_count())

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