From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752477AbcF1PSJ (ORCPT <rfc822;w@1wt.eu>);
	Tue, 28 Jun 2016 11:18:09 -0400
Received: from bhuna.collabora.co.uk ([46.235.227.227]:37949 "EHLO
	bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751879AbcF1PSH convert rfc822-to-8bit (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 28 Jun 2016 11:18:07 -0400
Date: Tue, 28 Jun 2016 12:17:52 -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>,
        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>
Subject: Re: [RFC v2 2/3] dma-buf/fence-array: add fence_array_teardown()
Message-ID: <20160628151752.GL2508@joana>
References: <1467055762-25881-1-git-send-email-gustavo@padovan.org>
 <1467055762-25881-3-git-send-email-gustavo@padovan.org>
 <577249CB.6050707@amd.com>
 <20160628141703.GJ2508@joana>
 <57729235.7040308@amd.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8BIT
In-Reply-To: <57729235.7040308@amd.com>
User-Agent: Mutt/1.6.1 (2016-04-27)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

2016-06-28 Christian König <christian.koenig@amd.com>:

> Am 28.06.2016 um 16:17 schrieb Gustavo Padovan:
> > 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.
> 
> No, there won't be any leak and you don't need to cleanup anything.
> 
> The fences contained in the fence array are already enabled for signaling.
> So they will eventually signal sooner or later and drop the reference to the
> fence array freeing it when the last one finished.
> 
> This was done to avoid the need to call fence_remove_callback() all the time
> on the fences in the array because of the warning on the function.

Right. I understand it now.

	Gustavo