Quoting Gustavo Padovan (2017-07-29 16:22:17)
> From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx>
> Cc: linux-kselftest@xxxxxxxxxxxxxxx
> Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>
>
> ---
> 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@xxxxxxxxxxxxxxxxxx>
-Chris
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