Fix PR libgomp/66761 and PR libgomp/67303 (tsan warnings)

Fix PR libgomp/66761 and PR libgomp/67303 (tsan warnings)

[VandeVondele Joost]

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The following fixes two warnings reported by tsan when running OMP'ed code. As suggested by Andrew Pinski in PR67303 for gomp_iter_guided_next, by employing a relaxed atomic load. The same pattern occurred a couple of more times, so fixed as well. I used the same approach for the warning in do_spin (PR66761), even though this is a different context.

Bootstrapped and regtested on x86_64-unknown-linux-gnu for trunk, and manually verified that the PR is fixed using a tsan compiled libgomp based on gcc-5.1.

OK for trunk ? 
This applies without changes to the 5 branch, should I commit there as well ?

libgomp/ChangeLog:

2015-08-22  Joost VandeVondele  <vondele@gnu.gcc.org>

        PR libgomp/66761
        PR libgomp/67303
        * iter.c (gomp_iter_dynamic_next): Employ an atomic load.
        (gomp_iter_guided_next): Idem.
        * iter_ull.c (gomp_iter_ull_dynamic_next): Idem.
        (gomp_iter_ull_guided_next): Idem.
        * config/linux/wait.h (do_spin): Idem.

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Index: libgomp/iter.c
===================================================================
--- libgomp/iter.c	(revision 227094)
+++ libgomp/iter.c	(working copy)
@@ -218,7 +218,7 @@ gomp_iter_dynamic_next (long *pstart, lo
 	}
     }
 
-  start = ws->next;
+  start = __atomic_load_n (&ws->next, MEMMODEL_RELAXED);
   while (1)
     {
       long left = end - start;
@@ -301,7 +301,7 @@ gomp_iter_guided_next (long *pstart, lon
   long start, end, nend, incr;
   unsigned long chunk_size;
 
-  start = ws->next;
+  start = __atomic_load_n (&ws->next, MEMMODEL_RELAXED);
   end = ws->end;
   incr = ws->incr;
   chunk_size = ws->chunk_size;
Index: libgomp/iter_ull.c
===================================================================
--- libgomp/iter_ull.c	(revision 227094)
+++ libgomp/iter_ull.c	(working copy)
@@ -219,7 +219,7 @@ gomp_iter_ull_dynamic_next (gomp_ull *ps
 	}
     }
 
-  start = ws->next_ull;
+  start = __atomic_load_n (&ws->next_ull, MEMMODEL_RELAXED);
   while (1)
     {
       gomp_ull left = end - start;
@@ -305,7 +305,7 @@ gomp_iter_ull_guided_next (gomp_ull *pst
   gomp_ull start, end, nend, incr;
   gomp_ull chunk_size;
 
-  start = ws->next_ull;
+  start = __atomic_load_n (&ws->next_ull, MEMMODEL_RELAXED);
   end = ws->end_ull;
   incr = ws->incr_ull;
   chunk_size = ws->chunk_size_ull;
Index: libgomp/config/linux/wait.h
===================================================================
--- libgomp/config/linux/wait.h	(revision 227094)
+++ libgomp/config/linux/wait.h	(working copy)
@@ -49,7 +49,8 @@ static inline int do_spin (int *addr, in
 {
   unsigned long long i, count = gomp_spin_count_var;
 
-  if (__builtin_expect (gomp_managed_threads > gomp_available_cpus, 0))
+  if (__builtin_expect (__atomic_load_n (&gomp_managed_threads,
+      MEMMODEL_RELAXED) > gomp_available_cpus, 0))
     count = gomp_throttled_spin_count_var;
   for (i = 0; i < count; i++)
     if (__builtin_expect (__atomic_load_n (addr, MEMMODEL_RELAXED) != val, 0))

Re: Fix PR libgomp/66761 and PR libgomp/67303 (tsan warnings)

[Jakub Jelinek]

On Sat, Aug 22, 2015 at 10:36:45AM +0000, VandeVondele  Joost wrote:
> OK for trunk ? 
> This applies without changes to the 5 branch, should I commit there as well ?

Ok, with a small change:

> 2015-08-22  Joost VandeVondele  <vondele@gnu.gcc.org>
> 
>         PR libgomp/66761
>         PR libgomp/67303
>         * iter.c (gomp_iter_dynamic_next): Employ an atomic load.
>         (gomp_iter_guided_next): Idem.
>         * iter_ull.c (gomp_iter_ull_dynamic_next): Idem.
>         (gomp_iter_ull_guided_next): Idem.
>         * config/linux/wait.h (do_spin): Idem.

> --- libgomp/config/linux/wait.h	(revision 227094)
> +++ libgomp/config/linux/wait.h	(working copy)
> @@ -49,7 +49,8 @@ static inline int do_spin (int *addr, in
>  {
>    unsigned long long i, count = gomp_spin_count_var;
>  
> -  if (__builtin_expect (gomp_managed_threads > gomp_available_cpus, 0))
> +  if (__builtin_expect (__atomic_load_n (&gomp_managed_threads,
> +      MEMMODEL_RELAXED) > gomp_available_cpus, 0))

Please fix up formatting here, MEMMODEL_RELAXED should be below
&gomp_managed_threads and most likely > will need to be below
__atomic_load_n.

>      count = gomp_throttled_spin_count_var;
>    for (i = 0; i < count; i++)
>      if (__builtin_expect (__atomic_load_n (addr, MEMMODEL_RELAXED) != val, 0))


	Jakub

RE: Fix PR libgomp/66761 and PR libgomp/67303 (tsan warnings)

[VandeVondele Joost]

Thanks, committed to trunk r227119 with the format fix. Do you want this on the 5 branch as well ?

Joost

Re: Fix PR libgomp/66761 and PR libgomp/67303 (tsan warnings)

[Jakub Jelinek]

On Mon, Aug 24, 2015 at 11:04:54AM +0000, VandeVondele  Joost wrote:
> Thanks, committed to trunk r227119 with the format fix. Do you want this on the 5 branch as well ?

It is ok for 5 branch too.

	Jakub