[PATCH 3/3] selftests: sync: add test that closes the fd before fence signal

[Shuah Khan]

On 07/31/2017 01:43 PM, Gustavo Padovan wrote:
> 2017-07-30 Chris Wilson <chris at chris-wilson.co.uk>:
> 
>> Quoting Gustavo Padovan (2017-07-29 16:22:17)
>>> From: Gustavo Padovan <gustavo.padovan at collabora.com>
>>>
>>> We found this bug in the sw_sync so adding a test case to prevent it to
>>> happen in the future.
>>>
>>> Cc: Shuah Khan <shuahkh at osg.samsung.com>
>>> Cc: linux-kselftest at vger.kernel.org
>>> Signed-off-by: Gustavo Padovan <gustavo.padovan at collabora.com>
>>>
>>> ---
>>> To be applied after the TAP13 convertion patches.
>>> ---
>>>  tools/testing/selftests/sync/sync_fence.c | 23 +++++++++++++++++++++++
>>>  tools/testing/selftests/sync/sync_test.c  |  1 +
>>>  tools/testing/selftests/sync/synctest.h   |  1 +
>>>  3 files changed, 25 insertions(+)
>>>
>>> diff --git a/tools/testing/selftests/sync/sync_fence.c b/tools/testing/selftests/sync/sync_fence.c
>>> index 13f1752..70cfa61 100644
>>> --- a/tools/testing/selftests/sync/sync_fence.c
>>> +++ b/tools/testing/selftests/sync/sync_fence.c
>>> @@ -29,6 +29,29 @@
>>>  #include "sw_sync.h"
>>>  #include "synctest.h"
>>>  
>>> +int test_close_fence_fd_before_inc(void)
>>> +{
>>> +       int fence, valid, ret;
>>> +       int timeline = sw_sync_timeline_create();
>>> +
>>> +       valid = sw_sync_timeline_is_valid(timeline);
>>> +       ASSERT(valid, "Failure allocating timeline\n");
>>> +
>>> +       fence = sw_sync_fence_create(timeline, "allocFence", 1);
>>> +       valid = sw_sync_fence_is_valid(fence);
>>> +       ASSERT(valid, "Failure allocating fence\n");
>>> +
>>
>> /*
>>  * We want the destroy + inc to run within the same RCU grace period so
>>  * that the zombie fence still exists on the timeline.
>>  */
>>
>>> +       sw_sync_fence_destroy(fence);
>>
>> I think this doesn't exercise the bug you found as we should be entering
>> the timeline_inc loop with fence.refcount==0 rather than the refcount
>> going to zero within the loop.
>>
>> To achieve that we need to find a callback that does unreference a
>> dma-fence and chain those together so that it frees a sw_sync from the
>> same timeline.
> 
> Indeed. Without the internal callback this test is a bit useless. We
> could test this under drm atomic tests on IGT. Particulary, I hit it
> playing with tests for v4l2 fences.
> 

Hi Gustavo,

Would you like this pulled into 4.14-rc1? Sounds like this test is for a
feature that doesn't exist yet?

thanks,
-- Shuah