[PATCH 1/9] drm/amdgpu:cleanup hw fence get&put

[Christian König]

NAK, we have tried this before.

This way we can accidentally try to signal a fence twice when the fence 
value is somehow corrupted.

Christian.

Am 25.10.2017 um 11:22 schrieb Monk Liu:
> In amdgpu_fence_process it shouldn't put the signaled hw fence and set
> RCU pointer to NULL, instead the more reasonable sequence is just leave
> the RCU be there untouched, and:
> 1) Either driver_fini() should put this RCU fence or
> 2) New hw fence emitting should take the RCU slot and put the old hw fence.
>
> mapping between get & put on hw fence is:
>
> Get						Put
> fence_emit:fence_init	--->	free_job:put job->fence
> 	       		--->	run_job:put job->fence //GPU RESET case
>
> fence_emit:rcu_assign_pointer	---> fence_driver_fini:put ring->fence_drv.fences[j]
> 				---> fence_emit:put(old) //after fence_wait(old)
>
> run_job:job->fence=fence_get()	--> sched_main:put(fence)
> 				--> job_recovery:put(fence) //for GPU RESET case
>
> sched_main:parent=fence_get()	--> sched_fence_free:put(fence->parent)
> sched_job_recovery:parent=fence_get() --> sched_hw_job_reset:put(s_job->s_fence->parent) // for GPU RESET case
>
> Change-Id: I623167c1e3143233f4e1be7a400a9b698b4a1355
> Signed-off-by: Monk Liu <Monk.Liu at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> index f43319c..d7374cf 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> @@ -161,6 +161,8 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f)
>   		dma_fence_wait(old, false);
>   	}
>   
> +	dma_fence_put(old);
> +
>   	rcu_assign_pointer(*ptr, dma_fence_get(&fence->base));
>   
>   	*f = &fence->base;
> @@ -246,7 +248,6 @@ void amdgpu_fence_process(struct amdgpu_ring *ring)
>   
>   		/* There is always exactly one thread signaling this fence slot */
>   		fence = rcu_dereference_protected(*ptr, 1);
> -		RCU_INIT_POINTER(*ptr, NULL);
>   
>   		if (!fence)
>   			continue;
> @@ -257,7 +258,6 @@ void amdgpu_fence_process(struct amdgpu_ring *ring)
>   		else
>   			BUG();
>   
> -		dma_fence_put(fence);
>   	} while (last_seq != seq);
>   }
>