linux-kernel - Re: [PATCH 0/7] kcsan: Introduce CONFIG_KCSAN

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Date:   Wed, 9 Jun 2021 16:48:33 +0200
From:   Marco Elver <elver@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] kcsan: Introduce CONFIG_KCSAN_PERMISSIVE

On Wed, 9 Jun 2021 at 14:38, Mark Rutland <mark.rutland@....com> wrote:
> Hi Marco,
>
> On Mon, Jun 07, 2021 at 02:56:46PM +0200, Marco Elver wrote:
> > While investigating a number of data races, we've encountered data-racy
> > accesses on flags variables to be very common. The typical pattern is a
> > reader masking all but one bit, and the writer setting/clearing only 1
> > bit (current->flags being a frequently encountered case; mm/sl[au]b.c
> > disables KCSAN for this reason currently).
>
> As a heads up, I just sent out the series I promised for
> thread_info::flags, at:
>
>   https://lore.kernel.org/lkml/20210609122001.18277-1-mark.rutland@arm.com/T/#t
>
> ... which I think is complementary to this (IIUC it should help with the
> multi-bit cases you mention below), and may help to make the checks more
> stringent in future.

Nice, glad to see this.

And yes, this series isn't a permission to let the 'flags' variables
be forgotten, but perhaps not every subsystem wants to go through this
now. So seeing any progress on this front helps and we can also use it
to give concrete suggestions how to approach it (e.g. your accessors).

> FWIW, for this series:
>
> Acked-by: Mark Rutland <mark.rutland@....com>

Thank you!