From: Thomas Rodgers <trodgers@redhat.com>
To: Mike Crowe <mac@mcrowe.com>
Cc: Jonathan Wakely <jwakely@redhat.com>,
libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: Re: [RFC] libstdc++: Do not use pthread_mutex_clocklock with ThreadSanitizer
Date: Thu, 11 May 2023 08:54:24 -0700 [thread overview]
Message-ID: <CAMmuTO8AZYXtwV1K=26jkPJNibgpBhv793neHF=XOy4p1SuPZw@mail.gmail.com> (raw)
In-Reply-To: <ZFzdW4gP0x/d+ghs@mcrowe.com>
[-- Attachment #1: Type: text/plain, Size: 2466 bytes --]
On Thu, May 11, 2023 at 5:21 AM Mike Crowe via Libstdc++ <
libstdc++@gcc.gnu.org> wrote:
> On Wednesday 10 May 2023 at 12:31:12 +0100, Jonathan Wakely wrote:
> > On Wed, 10 May 2023 at 12:20, Jonathan Wakely via Libstdc++ <
> > libstdc++@gcc.gnu.org> wrote:
> >
> > > This patch would avoid TSan false positives when using timed waiting
> > > functions on mutexes and condvars, but as noted below, it changes the
> > > semantics.
> > >
> > > I'm not sure whether we want this workaround in place until tsan gets
> > > fixed.
> > >
> > > On one hand, there's no guarantee that those functions use the right
> > > clock anyway (and they won't do unless a recent-ish glibc is used). But
> > > on the other hand, if they normally would use the right clock because
> > > you have glibc support, it's not ideal for tsan to cause a different
> > > clock to be used.
> > >
> >
> > But of course, it's not ideal to get false positives from tsan either
> > (especially when it looks like a libstdc++ bug, as initially reported to
> > me).
>
> I think that this is probably the least-worst option in the short term. As
> TSan is distributed with GCC this workaround can be removed as soon as its
> TSan implementation gains the necessary interceptors. I shall look into
> trying to do that.
>
>
I don't have a strong opinion either way on this, but I think documenting
the TSAN suppressions is the option most in keeping with the principle of
Least Astonishment.
> However, ...
>
> > > diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
> > > index 89e7f5f5f45..e2700b05ec3 100644
> > > --- a/libstdc++-v3/acinclude.m4
> > > +++ b/libstdc++-v3/acinclude.m4
> > > @@ -4284,7 +4284,7 @@ AC_DEFUN([GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT],
> [
> > > [glibcxx_cv_PTHREAD_COND_CLOCKWAIT=no])
> > > ])
> > > if test $glibcxx_cv_PTHREAD_COND_CLOCKWAIT = yes; then
> > > - AC_DEFINE(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT, 1, [Define if
> > > pthread_cond_clockwait is available in <pthread.h>.])
> > > + AC_DEFINE(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT, (_GLIBCXX_TSAN==0),
> > > [Define if pthread_cond_clockwait is available in <pthread.h>.])
> > > fi
>
> TSan does appear to have an interceptor for pthread_cond_clockwait, even if
> it lacks the others. Does this mean that this part is unnecessary?
>
> See: https://github.com/google/sanitizers/issues/1259
>
> Thanks.
>
> Mike.
>
>
next prev parent reply other threads:[~2023-05-11 15:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-10 11:20 Jonathan Wakely
2023-05-10 11:31 ` Jonathan Wakely
2023-05-11 12:19 ` Mike Crowe
2023-05-11 12:42 ` Jonathan Wakely
2023-05-11 20:52 ` [PATCH v2] " Jonathan Wakely
2023-05-12 10:30 ` Mike Crowe
2023-05-12 10:32 ` Jonathan Wakely
2023-05-15 12:03 ` Mike Crowe
2023-05-15 19:58 ` Thomas Rodgers
2023-05-11 15:54 ` Thomas Rodgers [this message]
2023-05-11 16:04 ` [RFC] " Jonathan Wakely
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