Re: [PATCH] kcov: simplify interrupt check

[Dmitry Vyukov]

On Tue, Mar 21, 2017 at 10:28 AM, Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> wrote:
>
> On March 21, 2017 5:10 PM Dmitry Vyukov wrote:
>>
>> @@ -60,15 +60,8 @@ void notrace __sanitizer_cov_trace_pc(void)
>>       /*
>>        * We are interested in code coverage as a function of a syscall inputs,
>>        * so we ignore code executed in interrupts.
>> -      * The checks for whether we are in an interrupt are open-coded, because
>> -      * 1. We can't use in_interrupt() here, since it also returns true
>> -      *    when we are inside local_bh_disable() section.
>> -      * 2. We don't want to use (in_irq() | in_serving_softirq() | in_nmi()),
>> -      *    since that leads to slower generated code (three separate tests,
>> -      *    one for each of the flags).
>>        */
>> -     if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
>> -                                                     | NMI_MASK)))
>> +     if (!t || !in_task())
>>               return;
>
> Nit: can we get the current task check cut off?


Humm... good question.
I don't remember why exactly I added it. I guess something was
crashing during boot. Note that this call is inserted into almost all
kernel code. But probably that was before I disabled instrumentation
of some early boot code for other reasons (with KCOV_INSTRUMENT := n
in Makefile), because now I can boot kernel in qemu without this
check. But I am still not sure about real hardware/arm/etc.
Does anybody know if current can ever (including early boot) return
invalid pointer?