[PATCH] dma-fence: fix dma_fence_get_rcu_safe

[Christian König]

Am 11.09.2017 um 12:01 schrieb Chris Wilson:
> [SNIP]
>> Yeah, but that is illegal with a fence objects.
>>
>> When anybody allocates fences this way it breaks at least
>> reservation_object_get_fences_rcu(),
>> reservation_object_wait_timeout_rcu() and
>> reservation_object_test_signaled_single().
> Many, many months ago I sent patches to fix them all.

Found those after a bit a searching. Yeah, those patches where proposed 
more than a year ago, but never pushed upstream.

Not sure if we really should go this way. dma_fence objects are shared 
between drivers and since we can't judge if it's the correct fence based 
on a criteria in the object (only the read counter which is outside) all 
drivers need to be correct for this.

I would rather go the way and change dma_fence_release() to wrap 
fence->ops->release into call_rcu() to keep the whole RCU handling 
outside of the individual drivers.

Regards,
Christian.