sw_sync deadlock avoidance, take 3

[Bas Nieuwenhuizen]

On Wed, Jul 15, 2020 at 12:34 PM Chris Wilson <chris at chris-wilson.co.uk> wrote:
>
> Quoting Bas Nieuwenhuizen (2020-07-15 11:23:35)
> > Hi Chris,
> >
> > My concern with going in this direction was that we potentially allow
> > an application to allocate a lot of kernel memory but not a lot of fds
> > by creating lots of fences and then closing the fds but never
> > signaling them. Is that not an issue?
>
> I did look to see if there was a quick way we could couple into the
> sync_file release itself to remove the syncpt from the timeline, but
> decided that for a debug feature, it wasn't a pressing concern.
>
> Maybe now is the time to ask: are you using sw_sync outside of
> validation?

Yes, this is used as part of the Android stack on Chrome OS (need to
see if ChromeOS specific, but
https://source.android.com/devices/graphics/sync#sync_timeline
suggests not)

> -Chris