Re: [PATCH v2] dma-buf/sw_sync: Optimize the retrieval of fence reference counts

[Christian König]

On 11/5/26 14:55, Danilo Krummrich wrote:
> On Thu Nov 5, 2026 at 11:03 AM CET, Christian König wrote:
>> On 11/5/26 06:27, Edward Adam Davis wrote:
>>> Fixes: e531fdb5cd5e ("dma-buf/sw_sync: Avoid recursive lock during fence signal")
>>
>> Please completely drop that. This is not something which has any justification to be backported.
> 
> Fixes: identifies the commit that introduced a bug for better reference,
> independently of whether the fix should be backported.
> 
> If something shouldn't be selected by autosel one can add
> 
> 	Cc: <stable+noautosel@xxxxxxxxxx> # reason to exclude from stable

Oh, thanks for that! I wasn't aware that this possibility exists as well.

> In this case I assume you said that because SW_SYNC is test infrastructure? If
> so, AFAIK the stable team explicitly does backport test infrastructure as people
> also run selftests on stable kernels.

Well yes and no. The situation is a bit more complicated, the point is that SW_SYNC is largely deprecated test infrastructure.

The provided functionality from SW_SYNC can intentionally hard crash the kernel without any chance to recover.

The patch is now fixing a bug which could potentially crash the kernel while using SW_SYNC, but for a component which does exactly that it is kind of pointless.

I mean it is nice to have for documentation purposes, but SW_SYNC is only still around because we don't want to break the uAPI and keep CI systems running.

And *YES*, SW_SYNC shouldn't have been merged in the first place.

Regards,
Christian.

> 
> Thanks,
> Danilo