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

[Chris Wilson]

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.

Still add the comment about what you are intending to hit here and
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris