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Date: Tue, 28 Jun 2016 11:17:03 -0300
From: Gustavo Padovan <gustavo.padovan@collabora.com>
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>,
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        Sumit Semwal <sumit.semwal@linaro.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Gustavo Padovan <gustavo.padovan@collabora.co.uk>,
        Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: [RFC v2 2/3] dma-buf/fence-array: add fence_array_teardown()
Message-ID: <20160628141703.GJ2508@joana>
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2016-06-28 Christian König <christian.koenig@amd.com>:

> Am 27.06.2016 um 21:29 schrieb Gustavo Padovan:
> > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > 
> > 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.
> 
> The fence array keeps a reference to itself as long as not all callbacks are
> signaled.
> 
> So you only need to unregister your callback from the array itself 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:

	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

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.

	Gustavo