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Subject[PATCH 4.19 168/276] drm/amdgpu: fix old fence check in amdgpu_fence_emit
Date
[ Upstream commit 3d2aca8c8620346abdba96c6300d2c0b90a1d0cc ]

We don't hold a reference to the old fence, so it can go away
any time we are waiting for it to signal.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 24 ++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
index 7056925eb3860..869ff624b108c 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
@@ -136,8 +136,9 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f,
{
struct amdgpu_device *adev = ring->adev;
struct amdgpu_fence *fence;
- struct dma_fence *old, **ptr;
+ struct dma_fence __rcu **ptr;
uint32_t seq;
+ int r;

fence = kmem_cache_alloc(amdgpu_fence_slab, GFP_KERNEL);
if (fence == NULL)
@@ -153,15 +154,24 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct dma_fence **f,
seq, flags | AMDGPU_FENCE_FLAG_INT);

ptr = &ring->fence_drv.fences[seq & ring->fence_drv.num_fences_mask];
+ if (unlikely(rcu_dereference_protected(*ptr, 1))) {
+ struct dma_fence *old;
+
+ rcu_read_lock();
+ old = dma_fence_get_rcu_safe(ptr);
+ rcu_read_unlock();
+
+ if (old) {
+ r = dma_fence_wait(old, false);
+ dma_fence_put(old);
+ if (r)
+ return r;
+ }
+ }
+
/* This function can't be called concurrently anyway, otherwise
* emitting the fence would mess up the hardware ring buffer.
*/
- old = rcu_dereference_protected(*ptr, 1);
- if (old && !dma_fence_is_signaled(old)) {
- DRM_INFO("rcu slot is busy\n");
- dma_fence_wait(old, false);
- }
-
rcu_assign_pointer(*ptr, dma_fence_get(&fence->base));

*f = &fence->base;
--
2.20.1


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