Am 22.05.21 um 04:57 schrieb Felix Kuehling:
When the BO gets individualized, there is an assumption that nobody is
accessing it any more. See this comment in ttm_bo_individualize_resv:
/* This works because the BO is about to be destroyed and nobody
* reference it any more. The only tricky case is the trylock on
* the resv object while holding the lru_lock.
*/
That is violated when the BO is still being swapped out at this stage.
You can kind of paper that over by taking the LRU lock. But there are
probably other race conditions going on when the reservation gets
swapped by "individualize" during an eviction.
I think to avoid all that TTM needs to make sure that the BO is no
longer on the LRU list when it gets individualized.
Exactly that is what we try to avoid because we want to keep the
position on the LRU the same.
Individualizing works because the swap and evict code ignores BOs with
zero reference count.
So yes I think Xinhui's patch should work fine.
Regards,
Christian.
Regards,
Felix
Am 2021-05-21 um 10:11 p.m. schrieb xinhui pan:
The reservation object might be locked again by evict/swap after
individualized. The race is like below.
cpu 0 cpu 1
BO release BO evict or swap
lock lru_lock
ttm_bo_individualize_resv {resv = &_resv}
ttm_bo_evict_swapout_allowable
dma_resv_trylock(resv)
->release_notify() {BUG_ON(!trylock(resv))}
if (!ttm_bo_get_unless_zero))
dma_resv_unlock(resv)
unlock lru_lock
To fix it simply, let's acquire lru_lock before resv trylock to avoid
the race above.
Signed-off-by: xinhui pan <xinhui.pan@xxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index 928e8d57cd08..8f6da0034db9 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -318,7 +318,9 @@ int amdgpu_amdkfd_remove_fence_on_pt_pd_bos(struct amdgpu_bo *bo)
ef = container_of(dma_fence_get(&info->eviction_fence->base),
struct amdgpu_amdkfd_fence, base);
+ spin_lock(&bo->tbo.bdev->lru_lock);
BUG_ON(!dma_resv_trylock(bo->tbo.base.resv));
+ spin_unlock(&bo->tbo.bdev->lru_lock);
ret = amdgpu_amdkfd_remove_eviction_fence(bo, ef);
dma_resv_unlock(bo->tbo.base.resv);
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