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From: "dvyukov at google dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug sanitizer/55561] TSAN: Fortran/OMP yields false positives
Date: Wed, 02 Jan 2013 09:09:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55561

--- Comment #29 from Dmitry Vyukov <dvyukov at google dot com> 2013-01-02 09:09:11 UTC ---
(In reply to comment #28)
> (In reply to comment #26)
> > For config/linux/ptrlock the changes are:
> > [...]
> 
> Following your suggestions, I applied the following patch (mistakes are mine),
> which allows me to run without warnings from libgomp:
> 
> Index: config/linux/wait.h
> ===================================================================
> --- config/linux/wait.h (revision 194730)
> +++ config/linux/wait.h (working copy)
> @@ -51,7 +51,7 @@
>    if (__builtin_expect (gomp_managed_threads > gomp_available_cpus, 0))
>      count = gomp_throttled_spin_count_var;
>    for (i = 0; i < count; i++)
> -    if (__builtin_expect (*addr != val, 0))
> +    if (__builtin_expect (__atomic_load_n(addr,MEMMODEL_RELAXED) != val, 0))
>        return 0;
>      else
>        cpu_relax ();
> Index: config/linux/ptrlock.c
> ===================================================================
> --- config/linux/ptrlock.c      (revision 194730)
> +++ config/linux/ptrlock.c      (working copy)
> @@ -50,9 +50,9 @@
>  #endif
>    do
>      do_wait (intptr, 2);
> -  while (*intptr == 2);
> +  while (__atomic_load_n(intptr, MEMMODEL_RELAXED) == 2);
>    __asm volatile ("" : : : "memory");
> -  return *ptrlock;
> +  return (void*)__atomic_load_n(ptrlock, MEMMODEL_ACQUIRE);
>  }
> 
>  void
> Index: config/linux/ptrlock.h
> ===================================================================
> --- config/linux/ptrlock.h      (revision 194730)
> +++ config/linux/ptrlock.h      (working copy)
> @@ -48,8 +48,9 @@
>  {
>    uintptr_t oldval;
> 
> -  if ((uintptr_t) *ptrlock > 2)
> -    return *ptrlock;
> +  uintptr_t v = (uintptr_t)__atomic_load_n(ptrlock, MEMMODEL_ACQUIRE);
> +  if (v > 2)
> +    return (void*)v;
> 
>    oldval = 0;
>    if (__atomic_compare_exchange_n (ptrlock, &oldval, 1, false,


Great!
Please post the patch to http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40362
I believe it is the correct fix for the bug.