linux-kernel - Re: [RFC 26/29] dma-buf/fence: remove pointless fence_timeline

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Date:	Tue, 9 Feb 2016 14:55:29 -0800
From:	Tom Cherry <tomcherry@...gle.com>
To:	Greg Hackmann <ghackmann@...gle.com>
Cc:	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	John Harrison <John.C.Harrison@...el.com>,
	Gustavo Padovan <gustavo@...ovan.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	dri-devel@...ts.freedesktop.org, daniels@...labora.com,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Rob Clark <robdclark@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	Dmitry Torokhov <dtor@...gle.com>
Subject: Re: [RFC 26/29] dma-buf/fence: remove pointless fence_timeline_signal
 at destroy phase

On Fri, Jan 15, 2016 at 3:42 PM, Greg Hackmann <ghackmann@...gle.com> wrote:
> On 01/15/2016 10:02 AM, Gustavo Padovan wrote:
>>
>> Patches 27 and 28 are attempt to fix that. I assumed that if some code is
>> calling fence_timeline_destroy() it wants to stop everything so I
>> worked on a solution that stops any waiter and allows the timeline to be
>> destroyed.
>>
>> No one is using fence_timeline_destroy() in mainline now, so it is
>> definately a behaviour we can discuss.
>>
>>         Gustavo
>>
>
> +Tom Cherry and Dmitry Torokhov recently discovered that this was broken by
> the refactoring of Android sync on top of dma-buf fences.
>
> Tom and Dmitry, did you send the proposed fix upstream?

There was a similar issue that I had originally thought to be related
to fence_timeline_destroy() but was actually related to
sync_fence_free().  Dmitry sent the patch upstream at
https://lkml.org/lkml/2015/12/14/953, but it does not look like it has
received any feedback.

We saw real panics without this patch.  I didn't see this patch or any
similar changes in the destaging commits, and I would recommend it be
looked at while destaging this driver.

Tom