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

[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);
 }
 
-- 
2.7.4