Re: [PATCH i-g-t v6 14/21] tests/sw_sync: Add subtest test_sync_expired_merge

[Robert Foss <robert.foss@collabora.com>]

On Thu, 2016-11-17 at 15:39 +0000, Chris Wilson wrote:
> On Thu, Nov 17, 2016 at 10:02:02AM -0500, robert.foss@collabora.com
> wrote:
> > 
> > From: Rafael Antognolli <rafael.antognolli@intel.com>
> > 
> > This test creates an already expired fence, then creates a merged
> > fence
> > out of that expired one (passed twice to the merge operation), and
> > finally closes the merged fence. It shows that if the refcounts are
> > wrong on the original expired fence, it might get freed while still
> > in
> > use. Usually a kernel panick will follow.
> > 
> > Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
> > Signed-off-by: Robert Foss <robert.foss@collabora.com>
> > ---
> >  tests/sw_sync.c | 28 ++++++++++++++++++++++++++++
> >  1 file changed, 28 insertions(+)
> > 
> > diff --git a/tests/sw_sync.c b/tests/sw_sync.c
> > index 4e52f48..65416ad 100644
> > --- a/tests/sw_sync.c
> > +++ b/tests/sw_sync.c
> > @@ -582,6 +582,31 @@ static void
> > test_sync_multi_producer_single_consumer(void)
> >  		pthread_join(threads[i], NULL);
> >  }
> >  
> > +static void test_sync_expired_merge(void)
> > +{
> > +	int iterations = 1 << 20;
> > +	int timeline;
> > +	int i;
> > +	int fence_expired, fence_merged;
> > +
> > +	timeline = sw_sync_timeline_create();
> > +
> > +	sw_sync_timeline_inc(timeline, 100);
> > +	fence_expired = sw_sync_fence_create(timeline, 1);
> igt_assert(sync_wait(fence_expired, 0) == 1);
> or
> igt_assert(fence_signaled(fence_expired));
> 
> Both illustrative of the setup, and tests them.

Agreed, I'll add it for v7.

> 
> > 
> > +	fence_merged = sync_merge(fence_expired, fence_expired);
> > +	close(fence_merged);
> > +
> > +	for (i = 0; i < iterations; i++) {
> > +		int fence = sync_merge(fence_expired,
> > fence_expired);
> > +
> > +		igt_assert_f(sync_wait(fence, -1) == 0,
> > +				     "Failure waiting on
> > fence\n");
> > +		close(fence);
> Is the millionth iteration more likely to fail than iteration 0?
> 
> There's no change in code coverage, so is it worth the extra
> iterations?

I don't know if it is more likely to fail or not, which is why multiple
iterations are tested.

If you can tell me with certainty that multiple iterations always will
behave the same way I would be happy to remove the multiple iterations.

Granted, there are a few other tests that also do stress testing as a
part of what they test. So maybe this is redundant either way?
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