Re: [PATCH v2] libstdc++: Do not use pthread_mutex_clocklock with ThreadSanitizer

[Mike Crowe <mac@mcrowe.com>]

On Friday 12 May 2023 at 11:32:56 +0100, Jonathan Wakely wrote:
> On Fri, 12 May 2023 at 11:30, Mike Crowe <mac@mcrowe.com> wrote:
> > On Thursday 11 May 2023 at 21:52:22 +0100, Jonathan Wakely wrote:
> > > On Thu, 11 May 2023 at 13:42, Jonathan Wakely <jwakely@redhat.com>
> > wrote:
> > > > On Thu, 11 May 2023 at 13:19, Mike Crowe <mac@mcrowe.com> wrote:
> > > >> 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?
> > > >>
> > > >
> > > > Ah good point, thanks. I grepped for clocklock but not clockwait.
> > > >
> > >
> > > In fact it seems like we don't need to change
> > > _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK either, because I don't get any
> > tsan
> > > warnings for that. It doesn't have interceptors for
> > > pthread_rwlock_{rd,wr}lock, but it doesn't complain anyway (maybe it's
> > > simply not instrumenting the rwlock functions at all?!)
> >
> > It looks like TSan does have interceptors for pthread_rwlock_timedrdlock
> > etc. I can't explain why this doesn't cause problems when libstdc++ uses
> > pthread_rwlock_clockrdlock etc.
> >
> 
> I think glibc has renamed the rwlock functions, and so the interceptors no
> longer work.
> 
> # ifdef __USE_XOPEN2K
> /* Try to acquire read lock for RWLOCK or return after specfied time.  */
> #  ifndef __USE_TIME_BITS64
> extern int pthread_rwlock_timedrdlock (pthread_rwlock_t *__restrict
> __rwlock,
>       const struct timespec *__restrict
>       __abstime) __THROWNL __nonnull ((1, 2));
> #  else
> #   ifdef __REDIRECT_NTHNL
> extern int __REDIRECT_NTHNL (pthread_rwlock_timedrdlock,
>                              (pthread_rwlock_t *__restrict __rwlock,
>                               const struct timespec *__restrict __abstime),
>                              __pthread_rwlock_timedrdlock64)
>     __nonnull ((1, 2));
> #   else
> #    define pthread_rwlock_timedrdlock __pthread_rwlock_timedrdlock64
> #   endif
> #  endif
> # endif
> 
> If glibc is really providing a function called
> __pthread_rwlock_timedrdlock64 then will tsan be able to intercept that?

I'm by no means an expert, but I would guess not. I suspect that the
renaming was introduced as part of the Y2038 fixes and TSan hasn't caught
up with them either.

Mike.