linux-kernel - Re: [PATCH] kcsan: Treat runtime as NMI-like with interrupt tracing

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Message-ID: <87pn7yxnjc.fsf@nanos>
Date:   Mon, 10 Aug 2020 22:18:31 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Marco Elver <elver@...gle.com>, elver@...gle.com,
        paulmck@...nel.org
Cc:     peterz@...radead.org, bp@...en8.de, mingo@...nel.org,
        mark.rutland@....com, dvyukov@...gle.com, glider@...gle.com,
        andreyknvl@...gle.com, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org,
        syzbot+8db9e1ecde74e590a657@...kaller.appspotmail.com
Subject: Re: [PATCH] kcsan: Treat runtime as NMI-like with interrupt tracing

Marco Elver <elver@...gle.com> writes:
> Since KCSAN instrumentation is everywhere, we need to treat the hooks
> NMI-like for interrupt tracing. In order to present an as 'normal' as
> possible context to the code called by KCSAN when reporting errors, we
> need to update the IRQ-tracing state.
>
> Tested: Several runs through kcsan-test with different configuration
> (PROVE_LOCKING on/off), as well as hours of syzbot testing with the
> original config that caught the problem (without CONFIG_PARAVIRT=y,
> which appears to cause IRQ state tracking inconsistencies even when
> KCSAN remains off, see Link).
>
> Link: https://lkml.kernel.org/r/0000000000007d3b2d05ac1c303e@google.com
> Fixes: 248591f5d257 ("kcsan: Make KCSAN compatible with new IRQ state tracking")
> Reported-by: syzbot+8db9e1ecde74e590a657@...kaller.appspotmail.com
> Co-developed-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Marco Elver <elver@...gle.com>
> ---
> Patch Note: This patch applies to latest mainline. While current
> mainline suffers from the above problem, the configs required to hit the
> issue are likely not enabled too often (of course with PROVE_LOCKING on;
> we hit it on syzbot though). It'll probably be wise to queue this as
> normal on -rcu, just in case something is still off, given the
> non-trivial nature of the issue. (If it should instead go to mainline
> right now as a fix, I'd like some more test time on syzbot.)

I'd rather stick it into mainline before -rc1.

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>