[RFC PATCH 1/2] dma-fence: Avoid establishing a locking order between fence classes

[Christian König]

Am 30.11.21 um 13:31 schrieb Thomas Hellström:
> [SNIP]
>> Other than that, I didn't investigate the nesting fails enough to say 
>> I can accurately review this. :)
>
> Basically the problem is that within enable_signaling() which is 
> called with the dma_fence lock held, we take the dma_fence lock of 
> another fence. If that other fence is a dma_fence_array, or a 
> dma_fence_chain which in turn tries to lock a dma_fence_array we hit a 
> splat.

Yeah, I already thought that you constructed something like that.

You get the splat because what you do here is illegal, you can't mix 
dma_fence_array and dma_fence_chain like this or you can end up in a 
stack corruption.

Regards,
Christian.

>
> But I'll update the commit message with a typical splat.
>
> /Thomas