Re: [PATCH] drm/amdkfd: Fix sparse __rcu annotation warnings

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On 2023-12-08 05:11, Christian König wrote:
Am 07.12.23 um 20:14 schrieb Felix Kuehling:

On 2023-12-05 17:20, Felix Kuehling wrote:
Properly mark kfd_process->ef as __rcu and consistently access it with
rcu_dereference_protected.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202312052245.yFpBSgNH-lkp@xxxxxxxxx/
Signed-off-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>

ping.

Christian, would you review this patch, please?

Looks a bit suspicious, especially the rcu_dereference_protected() use.

What is the static checker complaining about in the first place?
From
https://lore.kernel.org/oe-kbuild-all/202312052245.yFpBSgNH-lkp@xxxxxxxxx/:

drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_process.c:1671:9: sparse: sparse: incompatible types in comparison expression (different address spaces): >> drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_process.c:1671:9: sparse:
struct dma_fence [noderef] __rcu * >> drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_process.c:1671:9: sparse: struct dma_fence * ... >> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c:2765:36: sparse: sparse: incompatible types in comparison expression (different address spaces): >> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c:2765:36: sparse: struct dma_fence [noderef] __rcu * >> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c:2765:36: sparse: struct dma_fence * >> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c:2765:36: sparse: sparse: incompatible types in comparison expression (different address spaces): >> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c:2765:36: sparse: struct dma_fence [noderef] __rcu * >> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c:2765:36: sparse: struct dma_fence *

As far as I can tell, the reason is, that I'm using dma_fence_get_rcu_safe and rcu_replace_pointer to get and update kfd_process->ef, without annotating the fence pointers with __rcu. This patch fixes that by marking kfd_process->ef as an __rcu pointer. The only place that was dereferencing it directly was kfd_process_wq_release, where I added rcu_dereference_protected. The condition I'm using here is, that the process ref count is 0 at that point, which means nobody else is referencing the process or this fence pointer at the time.

Regards,
  Felix



Regards,
Christian.


Thanks,
  Felix



---
  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h       | 2 +-
  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 4 ++--
  drivers/gpu/drm/amd/amdkfd/kfd_priv.h            | 2 +-
  drivers/gpu/drm/amd/amdkfd/kfd_process.c         | 6 ++++--
  4 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
index f2e920734c98..20cb266dcedd 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
@@ -314,7 +314,7 @@ void amdgpu_amdkfd_gpuvm_unmap_gtt_bo_from_kernel(struct kgd_mem *mem);   int amdgpu_amdkfd_map_gtt_bo_to_gart(struct amdgpu_device *adev, struct amdgpu_bo *bo);
    int amdgpu_amdkfd_gpuvm_restore_process_bos(void *process_info,
-                        struct dma_fence **ef);
+                        struct dma_fence __rcu **ef);
  int amdgpu_amdkfd_gpuvm_get_vm_fault_info(struct amdgpu_device *adev,
                            struct kfd_vm_fault_info *info);
  int amdgpu_amdkfd_gpuvm_import_dmabuf_fd(struct amdgpu_device *adev, int fd, diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index 7d91f99acb59..8ba6f6c8363d 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -2806,7 +2806,7 @@ static void amdgpu_amdkfd_restore_userptr_worker(struct work_struct *work)
      put_task_struct(usertask);
  }
  -static void replace_eviction_fence(struct dma_fence **ef,
+static void replace_eviction_fence(struct dma_fence __rcu **ef,
                     struct dma_fence *new_ef)
  {
      struct dma_fence *old_ef = rcu_replace_pointer(*ef, new_ef, true
@@ -2841,7 +2841,7 @@ static void replace_eviction_fence(struct dma_fence **ef,
   * 7.  Add fence to all PD and PT BOs.
   * 8.  Unreserve all BOs
   */
-int amdgpu_amdkfd_gpuvm_restore_process_bos(void *info, struct dma_fence **ef) +int amdgpu_amdkfd_gpuvm_restore_process_bos(void *info, struct dma_fence __rcu **ef)
  {
      struct amdkfd_process_info *process_info = info;
      struct amdgpu_vm *peer_vm;
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
index 45366b4ca976..5a24097a9f28 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
@@ -917,7 +917,7 @@ struct kfd_process {
       * fence will be triggered during eviction and new one will be created
       * during restore
       */
-    struct dma_fence *ef;
+    struct dma_fence __rcu *ef;
        /* Work items for evicting and restoring BOs */
      struct delayed_work eviction_work;
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
index 71df51fcc1b0..14b11d61f8dd 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
@@ -1110,6 +1110,8 @@ static void kfd_process_wq_release(struct work_struct *work)
  {
      struct kfd_process *p = container_of(work, struct kfd_process,
                           release_work);
+    struct dma_fence *ef = rcu_dereference_protected(p->ef,
+        kref_read(&p->ref) == 0);
        kfd_process_dequeue_from_all_devices(p);
      pqm_uninit(&p->pqm);
@@ -1118,7 +1120,7 @@ static void kfd_process_wq_release(struct work_struct *work)
       * destroyed. This allows any BOs to be freed without
       * triggering pointless evictions or waiting for fences.
       */
-    dma_fence_signal(p->ef);
+    dma_fence_signal(ef);
        kfd_process_remove_sysfs(p);
  @@ -1127,7 +1129,7 @@ static void kfd_process_wq_release(struct work_struct *work)
      svm_range_list_fini(p);
        kfd_process_destroy_pdds(p);
-    dma_fence_put(p->ef);
+    dma_fence_put(ef);
        kfd_event_free_process(p);





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