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From:   Marco Elver <elver@google.com>
Date:   Thu, 17 Oct 2019 09:49:27 +0200
Message-ID: <CANpmjNPKbCrL+XzmMrnjqw+EYOa2H94cgE5sPJeuVONbCSqBHg@mail.gmail.com>
Subject: Re: [PATCH 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Alexander Potapenko <glider@google.com>,
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On Thu, 17 Oct 2019 at 09:47, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Wed, Oct 16, 2019 at 09:34:05PM +0200, Marco Elver wrote:
> > On Wed, 16 Oct 2019 at 20:44, Peter Zijlstra <peterz@infradead.org> wrote:
> > > > +     /*
> > > > +      * Disable interrupts & preemptions, to ignore races due to accesses in
> > > > +      * threads running on the same CPU.
> > > > +      */
> > > > +     local_irq_save(irq_flags);
> > > > +     preempt_disable();
> > >
> > > Is there a point to that preempt_disable() here?
> >
> > We want to avoid being preempted while the watchpoint is set up;
> > otherwise, we would report data-races for CPU-local data, which is
> > incorrect.
>
> Disabling IRQs already very much disables preemption. There is
> absolutely no point in doing preempt_disable() when the whole section
> already runs with IRQs disabled.

Ah thanks for the clarification, in that case I assume it's safe to
remove preempt_disable() for v2.

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