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

[Felix Kuehling <felix.kuehling@amd.com>]

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@intel.com>
>>> Closes: 
>>> https://lore.kernel.org/oe-kbuild-all/202312052245.yFpBSgNH-lkp@intel.com/
>>> Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
>>
>> 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@intel.com/:

>> 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);
>