Re: Kernel Concurrency Sanitizer (KCSAN)

Marco Elver
2019-10-02T19:52:12Z

Hi Joel,

On Tue, 1 Oct 2019 at 23:19, Joel Fernandes <joel@joelfernandes.org> wrote:
>
> 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?

This might be interesting at first, but it's not entirely clear how
feasible it is. It's also dangerous, because the real issue would be
ignored. It may be that one compiler version on a particular
architecture generates the same code, but any change in compiler or
architecture and this would no longer be true. Let me know if you have
any more ideas.

Best,
-- Marco

> Also appreciate a CC on future patches as well.
>
> thanks,
>
> - Joel
>
>
> >
> > Feel free to test and send feedback.
> >
> > Thanks,
> > -- Marco
>
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