From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gustavo Padovan <gustavo.padovan@collabora.com>
Subject: Re: [RFC v2 2/3] dma-buf/fence-array: add fence_array_teardown()
Date: Tue, 28 Jun 2016 12:17:52 -0300
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To: Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Cc: Gustavo Padovan <gustavo@padovan.org>, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Daniel Stone <daniels@collabora.com>, Daniel Vetter <daniel.vetter@ffwll.ch>, Rob Clark <robdclark@gmail.com>, Greg Hackmann <ghackmann@google.com>, John Harrison <John.C.Harrison@Intel.com>, laurent.pinchart@ideasonboard.com, seanpaul@google.com, marcheu@google.com, m.chehab@samsung.com, Sumit Semwal <sumit.semwal@linaro.org>, Maarten Lankhorst <maarten.lankhorst@linux.intel.com>, Chris Wilson <chris@chris-wilson.co.uk>
List-Id: dri-devel@lists.freedesktop.org

2016-06-28 Christian K=F6nig <christian.koenig@amd.com>:

> Am 28.06.2016 um 16:17 schrieb Gustavo Padovan:
> > 2016-06-28 Christian K=F6nig <christian.koenig@amd.com>:
> >=20
> > > Am 27.06.2016 um 21:29 schrieb Gustavo Padovan:
> > > > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > >=20
> > > > As the array of fence callbacks held by an active struct fence_=
array
> > > > each has a reference to the struct fence_array, when the owner =
of the
> > > > fence_array is freed it must dispose of the callback references=
 before
> > > > it can free the fence_array. This can not happen simply during
> > > > fence_release() because of the extra references and so we need =
a new
> > > > function to run before the final fence_put().
> > > As I said previously as well, this is completely superfluous.
> > >=20
> > > The fence array keeps a reference to itself as long as not all ca=
llbacks are
> > > signaled.
> > >=20
> > > So you only need to unregister your callback from the array itsel=
f and drop
> > > your reference when you don't need it any more in the sync file.
> > Exactly, this should be called from sync_file_free() because of the
> > following use case:
> >=20
> > 	1. You create 2 sync_file with 1 fence each
> > 	2. Merge both fences, which creates a fence array
> > 	3. Close the sync_file fd without waiting for the fences to
> > 	signal
> >=20
> > At this point you leak the fence-array because the final fence_put(=
)
> > does not release it because of the extra references from the non
> > signalled fences so we need to clean up this somehow.
>=20
> No, there won't be any leak and you don't need to cleanup anything.
>=20
> The fences contained in the fence array are already enabled for signa=
ling.
> So they will eventually signal sooner or later and drop the reference=
 to the
> fence array freeing it when the last one finished.
>=20
> This was done to avoid the need to call fence_remove_callback() all t=
he time
> on the fences in the array because of the warning on the function.

Right. I understand it now.

	Gustavo