Re: [WIP] Re: [PATCH] openmp: Fix intermittent hanging of task-detach-6 libgomp tests [PR98738]

[Thomas Schwinge <thomas@codesourcery.com>]

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Hi!

On 2021-04-09T13:00:39+0200, I wrote:
> On 2021-03-25T12:02:15+0100, I wrote:
>> On 2021-03-11T17:52:55+0100, I wrote:
>>> On 2021-02-23T22:52:38+0100, Jakub Jelinek via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>>>> On Tue, Feb 23, 2021 at 09:43:51PM +0000, Kwok Cheung Yeung wrote:
>>>>> On 19/02/2021 7:12 pm, Kwok Cheung Yeung wrote:
>>>>> > I have included the current state of my patch. All task-detach-* tests
>>>>> > pass when executed without offloading or with offloading to GCN, but
>>>>> > with offloading to Nvidia, task-detach-6.* hangs consistently but
>>>>> > everything else passes (probably because of the missing
>>>>> > gomp_team_barrier_done?).
>>>>>
>>>>> It looks like the hang has nothing to do with the detach patch - this hangs
>>>>> consistently for me when offloaded to NVPTX:
>>>>>
>>>>> #include <omp.h>
>>>>>
>>>>> int main (void)
>>>>> {
>>>>> #pragma omp target
>>>>>   #pragma omp parallel
>>>>>     #pragma omp task
>>>>>       ;
>>>>> }
>>>>>
>>>>> This doesn't hang when offloaded to GCN or the host device, or if
>>>>> num_threads(1) is specified on the omp parallel.
>>>
>>> So, I reproduced this the hard way;
>>> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98738#c13> :-/
>>>
>>> Please always file issues when you run into such things.  I've now filed
>>> PR99555 "[OpenMP/nvptx] Execution-time hang for simple nested OpenMP
>>> 'target'/'parallel'/'task' constructs".
>>>
>>>> Then it can be solved separately, I'll try to have a look if I see something
>>>> bad from the dumps, but I admit I don't have much experience with debugging
>>>> NVPTX offloaded code...
>>>
>>> Any luck?
>>>
>>>
>>> Until this gets resolved properly, OK to push something like the attached
>>> (currently testing) "Avoid OpenMP/nvptx execution-time hangs for simple
>>> nested OpenMP 'target'/'parallel'/'task' constructs [PR99555]"?
>>
>> As posted, I've now pushed "Avoid OpenMP/nvptx execution-time hangs for
>> simple nested OpenMP 'target'/'parallel'/'task' constructs [PR99555]" to
>> master branch in commit d99111fd8e12deffdd9a965ce17e8a760d531ec3, see
>> attached.  "... awaiting proper resolution, of course."
>
>> +  if (on_device_arch_nvptx ())
>> +    __builtin_abort (); //TODO Until resolved, skip, with error status.
>
> Actually, we can do better: do try to execute this trivial OpenMP code
> (expected to complete in no time), but for nvptx offloading "make sure
> that we exit quickly, with error status", and XFAIL that.  So that we'll
> get XFAIL -> XPASS when this starts to work for nvptx offloading.

Pushed "XFAIL OpenMP/nvptx execution-time hangs for simple nested OpenMP
'target'/'parallel'/'task' constructs [PR99555]" to master branch in
commit 4dd9e1c541e0eb921d62c8652c854b1259e56aac, see attached.


Grüße
 Thomas


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From 4dd9e1c541e0eb921d62c8652c854b1259e56aac Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@codesourcery.com>
Date: Wed, 7 Apr 2021 10:36:36 +0200
Subject: [PATCH] XFAIL OpenMP/nvptx execution-time hangs for simple nested
 OpenMP 'target'/'parallel'/'task' constructs [PR99555]

... still awaiting proper resolution, of course.

	libgomp/
	PR target/99555
	* testsuite/lib/libgomp.exp
	(check_effective_target_offload_device_nvptx): New.
	* testsuite/libgomp.c/pr99555-1.c <nvptx offload device>: Until
	resolved, make sure that we exit quickly, with error status,
	XFAILed.
	* testsuite/libgomp.c-c++-common/task-detach-6.c: Likewise.
	* testsuite/libgomp.fortran/task-detach-6.f90: Likewise.
---
 libgomp/testsuite/lib/libgomp.exp                    | 12 ++++++++++++
 .../testsuite/libgomp.c-c++-common/task-detach-6.c   |  5 ++++-
 libgomp/testsuite/libgomp.c/pr99555-1.c              |  5 ++++-
 libgomp/testsuite/libgomp.fortran/task-detach-6.f90  |  3 ++-
 4 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/libgomp/testsuite/lib/libgomp.exp b/libgomp/testsuite/lib/libgomp.exp
index 72d001186a5..14dcfdfd00a 100644
--- a/libgomp/testsuite/lib/libgomp.exp
+++ b/libgomp/testsuite/lib/libgomp.exp
@@ -401,6 +401,18 @@ proc check_effective_target_offload_device_shared_as { } {
     } ]
 }
 
+# Return 1 if using nvptx offload device.
+proc check_effective_target_offload_device_nvptx { } {
+    return [check_runtime_nocache offload_device_nvptx {
+      #include <omp.h>
+      #include "testsuite/libgomp.c-c++-common/on_device_arch.h"
+      int main ()
+	{
+	  return !on_device_arch_nvptx ();
+	}
+    } ]
+}
+
 # Return 1 if at least one Nvidia GPU is accessible.
 
 proc check_effective_target_openacc_nvidia_accel_present { } {
diff --git a/libgomp/testsuite/libgomp.c-c++-common/task-detach-6.c b/libgomp/testsuite/libgomp.c-c++-common/task-detach-6.c
index 119d7f52f8f..f18b57bf047 100644
--- a/libgomp/testsuite/libgomp.c-c++-common/task-detach-6.c
+++ b/libgomp/testsuite/libgomp.c-c++-common/task-detach-6.c
@@ -2,6 +2,8 @@
 
 #include <omp.h>
 #include <assert.h>
+#include <unistd.h> // For 'alarm'.
+
 #include "on_device_arch.h"
 
 /* Test tasks with detach clause on an offload device.  Each device
@@ -12,7 +14,8 @@ int main (void)
 {
   //TODO See '../libgomp.c/pr99555-1.c'.
   if (on_device_arch_nvptx ())
-    __builtin_abort (); //TODO Until resolved, skip, with error status.
+    alarm (4); /*TODO Until resolved, make sure that we exit quickly, with error status.
+		 { dg-xfail-run-if "PR99555" { offload_device_nvptx } } */
 
   int x = 0, y = 0, z = 0;
   int thread_count;
diff --git a/libgomp/testsuite/libgomp.c/pr99555-1.c b/libgomp/testsuite/libgomp.c/pr99555-1.c
index 0dc17bfa337..bd33b93716b 100644
--- a/libgomp/testsuite/libgomp.c/pr99555-1.c
+++ b/libgomp/testsuite/libgomp.c/pr99555-1.c
@@ -2,12 +2,15 @@
 
 // { dg-additional-options "-O0" }
 
+#include <unistd.h> // For 'alarm'.
+
 #include "../libgomp.c-c++-common/on_device_arch.h"
 
 int main (void)
 {
   if (on_device_arch_nvptx ())
-    __builtin_abort (); //TODO Until resolved, skip, with error status.
+    alarm (4); /*TODO Until resolved, make sure that we exit quickly, with error status.
+		 { dg-xfail-run-if "PR99555" { offload_device_nvptx } } */
 
 #pragma omp target
 #pragma omp parallel // num_threads(1)
diff --git a/libgomp/testsuite/libgomp.fortran/task-detach-6.f90 b/libgomp/testsuite/libgomp.fortran/task-detach-6.f90
index bd0beb63179..e4373b4c6f1 100644
--- a/libgomp/testsuite/libgomp.fortran/task-detach-6.f90
+++ b/libgomp/testsuite/libgomp.fortran/task-detach-6.f90
@@ -21,7 +21,8 @@ program task_detach_6
 
   !TODO See '../libgomp.c/pr99555-1.c'.
   if (on_device_arch_nvptx () /= 0) then
-     error stop !TODO Until resolved, skip, with error status.
+     call alarm (4, 0); !TODO Until resolved, make sure that we exit quickly, with error status.
+     ! { dg-xfail-run-if "PR99555" { offload_device_nvptx } }
   end if
 
   !$omp target map (tofrom: x, y, z) map (from: thread_count)
-- 
2.30.2