[llvm-dev] [ThreadSanitizer] Get deadlocks working

[Kostya Serebryany via llvm-dev]

On Tue, Sep 8, 2015 at 12:15 AM, Dmitry Vyukov via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> +thread-sanitizer mailing list
>
> On Mon, Sep 7, 2015 at 6:41 PM, Vaivaswatha Nagaraj <vn at compilertree.com>
> wrote:
> > Hi,
> >
> > I am interested in understand the compiler-rt thread sanitizer tool and
> have
> > recently started experimenting with it. In particular, I'm interested in
> the
> > deadlock detector.
> >
> > I see that deadlock detection currently don't work. (I tried with a few
> > simple deadlocks, as well as the test case "must_deadlock.cc" that is in
> the
> > test-suite). I understand from the comments that this is because the real
> > pthread_mutex_lock() is called before the handler (MutexLock()) in tsan.
> >
> > 1. Is there any particular reason that this interceptor is designed this
> > way? Can there be a callback prior to calling the real
> pthread_mutex_lock()
> > that can, for example, detect deadlocks?
> > 2. Upon debugging a simple test case, I see that there is a worker thread
> > that is created. Can this worker not check for the deadlock when the
> actual
> > threads are deadlocked.
>
> Hello Vaivaswatha,
>
> Yes, tsan currently detects only _potential_ deadlocks. On actual
> deadlocks it deadlocks as well.
> This is just not implemented yet.


Correct, I just did not have time to implement this.
In practice this is not the most important thing to have because
if the deadlock has actually happened in a test it is easy to find.
The potential deadlocks are more important.
Yet I fully agree this needs to be implemented.

--kcc



> Yes, mutex callback needs to be
> split into pre and post parts. The deadlock detector already has
> separate callbacks for these events, it is just a matter of threading
> these callbacks through tsan code.
> You can look at the standalone deadlock detector in
> lib/tsan/dd/dd_interceptors.cc, it does it correctly.
>
> --
> Dmitry Vyukov, Software Engineer, dvyukov at google.com
> Google Germany GmbH, Dienerstraße 12, 80331, München
> Geschäftsführer: Graham Law, Christine Elizabeth Flores
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
> Diese E-Mail ist vertraulich. Wenn Sie nicht der richtige Adressat
> sind, leiten Sie diese bitte nicht weiter, informieren Sie den
> Absender und löschen Sie die E-Mail und alle Anhänge. Vielen Dank.
> This e-mail is confidential. If you are not the right addressee please
> do not forward it, please inform the sender, and please erase this
> e-mail including any attachments. Thanks.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150908/a57676d2/attachment.html>