linux-kernel - Re: Kernel Concurrency Sanitizer (KCSAN)

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Date:   Tue, 1 Oct 2019 17:19:48 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Marco Elver <elver@...gle.com>
Cc:     kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Alexander Potapenko <glider@...gle.com>, paulmck@...ux.ibm.com,
        Paul Turner <pjt@...gle.com>, Daniel Axtens <dja@...ens.net>,
        Anatol Pomazau <anatol@...gle.com>,
        Will Deacon <willdeacon@...gle.com>,
        Andrea Parri <parri.andrea@...il.com>,
        stern@...land.harvard.edu, akiyks@...il.com, npiggin@...il.com,
        boqun.feng@...il.com, dlustig@...dia.com, j.alglave@....ac.uk,
        luc.maranget@...ia.fr
Subject: Re: Kernel Concurrency Sanitizer (KCSAN)

On Fri, Sep 20, 2019 at 04:18:57PM +0200, Marco Elver wrote:
> Hi all,
> 
> We would like to share a new data-race detector for the Linux kernel:
> Kernel Concurrency Sanitizer (KCSAN) --
> https://github.com/google/ktsan/wiki/KCSAN  (Details:
> https://github.com/google/ktsan/blob/kcsan/Documentation/dev-tools/kcsan.rst)
> 
> To those of you who we mentioned at LPC that we're working on a
> watchpoint-based KTSAN inspired by DataCollider [1], this is it (we
> renamed it to KCSAN to avoid confusion with KTSAN).
> [1] http://usenix.org/legacy/events/osdi10/tech/full_papers/Erickson.pdf
> 
> In the coming weeks we're planning to:
> * Set up a syzkaller instance.
> * Share the dashboard so that you can see the races that are found.
> * Attempt to send fixes for some races upstream (if you find that the
> kcsan-with-fixes branch contains an important fix, please feel free to
> point it out and we'll prioritize that).
> 
> There are a few open questions:
> * The big one: most of the reported races are due to unmarked
> accesses; prioritization or pruning of races to focus initial efforts
> to fix races might be required. Comments on how best to proceed are
> welcome. We're aware that these are issues that have recently received
> attention in the context of the LKMM
> (https://lwn.net/Articles/793253/).
> * How/when to upstream KCSAN?

Looks exciting. I think based on our discussion at LPC, you mentioned
one way of pruning is if the compiler generated different code with _ONCE
annotations than what would have otherwise been generated. Is that still on
the table, for the purposing of pruning the reports?

Also appreciate a CC on future patches as well.

thanks,

 - Joel


> 
> Feel free to test and send feedback.
> 
> Thanks,
> -- Marco