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

[Gustavo Padovan <gustavo.padovan@collabora.com>]

Hi Shuah,

On Wed, 2017-08-02 at 13:45 -0600, Shuah Khan wrote:
> On 07/31/2017 01:43 PM, Gustavo Padovan wrote:
> > 2017-07-30 Chris Wilson <chris@chris-wilson.co.uk>:
> > 
> > > Quoting Gustavo Padovan (2017-07-29 16:22:17)
> > > > From: Gustavo Padovan <gustavo.padovan@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@osg.samsung.com>
> > > > Cc: linux-kselftest@vger.kernel.org
> > > > Signed-off-by: Gustavo Padovan <gustavo.padovan@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?

It is for the current code, but I need to find a better way to trigger
what I want. I'll rethink this test and resend.

Gustavo

-- 
Gustavo Padovan
Collabora Ltd.
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