diff mbox

Fix sporadic failure in g++.dg/tsan/aligned_vs_unaligned_race.C

Message ID DUB118-W320D3B28DB527B0F27FCDE45B0@phx.gbl
State New
Headers show

Commit Message

Bernd Edlinger Jan. 4, 2015, 10:19 p.m. UTC 
On Sun, 4 Jan 2015 13:57:38, Mike Stump wrote:
>
> On Jan 4, 2015, at 1:48 PM, Bernd Edlinger <bernd.edlinger@hotmail.de> wrote:
>> I would need a way to link the test case two helper functions, that are not compiled with -fsanitize=thread
>
> /* { dg-additional-sources “tsan-helper.c" } */
>
> might be one step forward to do that. I don’t know off hand about the options. I think you may be able to specify unique options per file.
>
>> I tried, it and it works 10.000 times without one failure.
>
> So, statistically knowing it works in practice is nice. However, the standard is, does is work by design? I’ll let you comment on that. The sync approach I designed to work in any case, no matter the complexity, by design. I’d assume that you’ve engineered it to work by design.

IMO Yes, but Dmitry may know better. Tsan does not acquire a mutex _before_ it detects a race.
And race conditions that happen exactly synchronous may be invisible.

If we use some hidden mechanism to ensure that certain events happen in a certain sequence,
that would make a big difference. It would work much better than sleep(), we only need sleep if
we need to see the "as if synchronized via sleep" diagnostic.

I see now, that our tsan tests are almost verbatim copies of the LLVM test suite.

They _do_ have problems with the stability of positive tests, especially under stress,
I see all positive tests are called by a "deflake" tool, that exercises the test 10 times,
until it eventually succeeds.

I see one other test (which we apparently do not have here),
was changed recently from sleep(2) to sleep(4)

[Tsan] Fix the atomic_race.cc test to pass on systems with high loads
Differential Revision: http://reviews.llvm.org/D6478




Thanks
Bernd.
diff mbox

Patch

--- compiler-rt/trunk/test/tsan/atomic_race.cc  2014/05/30 14:08:51     209898
+++ compiler-rt/trunk/test/tsan/atomic_race.cc  2014/12/02 15:04:39     223122
@@ -36,7 +36,7 @@ 
   for (int i = 0; i < kTestCount; i++) {
     Test(i, &atomics[i], false);
   }
-  sleep(2);
+  sleep(4);
   for (int i = 0; i < kTestCount; i++) {
     fprintf(stderr, "Test %d reverse\n", i);
     Test(i, &atomics[kTestCount + i], false);