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Subject: Re: [PATCH] kcov: properly check if we are in an interrupt
To: Dmitry Vyukov <dvyukov@google.com>,
        Peter Zijlstra <peterz@infradead.org>
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Cc: Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Nicolai Stange <nicstange@gmail.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Kees Cook <keescook@chromium.org>, James Morse <james.morse@arm.com>,
        LKML <linux-kernel@vger.kernel.org>,
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        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>
From: Vegard Nossum <vegard.nossum@oracle.com>
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Date: Tue, 27 Sep 2016 13:20:46 +0200
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On 09/27/2016 09:50 AM, Dmitry Vyukov wrote:
> On Tue, Sep 27, 2016 at 9:34 AM, Peter Zijlstra <peterz@infradead.org> 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