[PATCH] dma-buf: fix and rework dma_buf_poll v7

[Christian König]

Totally forgotten to ping once more about that.

Michel has tested this now and I think we should push it ASAP. So can I 
get an rb?

Thanks,
Christian.

Am 23.07.21 um 10:04 schrieb Michel Dänzer:
> On 2021-07-20 3:11 p.m., Christian König wrote:
>> Daniel pointed me towards this function and there are multiple obvious problems
>> in the implementation.
>>
>> First of all the retry loop is not working as intended. In general the retry
>> makes only sense if you grab the reference first and then check the sequence
>> values.
>>
>> Then we should always also wait for the exclusive fence.
>>
>> It's also good practice to keep the reference around when installing callbacks
>> to fences you don't own.
>>
>> And last the whole implementation was unnecessary complex and rather hard to
>> understand which could lead to probably unexpected behavior of the IOCTL.
>>
>> Fix all this by reworking the implementation from scratch. Dropping the
>> whole RCU approach and taking the lock instead.
>>
>> Only mildly tested and needs a thoughtful review of the code.
>>
>> v2: fix the reference counting as well
>> v3: keep the excl fence handling as is for stable
>> v4: back to testing all fences, drop RCU
>> v5: handle in and out separately
>> v6: add missing clear of events
>> v7: change coding style as suggested by Michel, drop unused variables
>>
>> Signed-off-by: Christian König <christian.koenig at amd.com>
>> CC: stable at vger.kernel.org
> Working fine with https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1880
>
> Tested-by: Michel Dänzer <mdaenzer at redhat.com>
>
>