[AMD Official Use Only - AMD Internal Distribution Only]
>-----Original Message-----
>From: Kuehling, Felix <Felix.Kuehling@xxxxxxx>
>Sent: Saturday, January 4, 2025 7:18 AM
>To: Deng, Emily <Emily.Deng@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx; Yang,
>Philip <Philip.Yang@xxxxxxx>; Koenig, Christian <Christian.Koenig@xxxxxxx>
>Subject: Re: [PATCH v2] drm/amdgpu: Fix the looply call svm_range_restore_pages
>issue
>
>
>On 2025-01-02 21:26, Emily Deng wrote:
>> As the delayed free pt, the wanted freed bo has been reused which will
>> cause unexpected page fault, and then call svm_range_restore_pages.
>>
>> Detail as below:
>> 1.It wants to free the pt in follow code, but it is not freed
>> immediately and used “schedule_work(&vm->pt_free_work);”.
>>
>> [ 92.276838] Call Trace:
>> [ 92.276841] dump_stack+0x63/0xa0
>> [ 92.276887] amdgpu_vm_pt_free_list+0xfb/0x120 [amdgpu]
>> [ 92.276932] amdgpu_vm_update_range+0x69c/0x8e0 [amdgpu]
>> [ 92.276990] svm_range_unmap_from_gpus+0x112/0x310 [amdgpu]
>> [ 92.277046] svm_range_cpu_invalidate_pagetables+0x725/0x780 [amdgpu]
>> [ 92.277050] ? __alloc_pages_nodemask+0x19f/0x3e0
>> [ 92.277051] mn_itree_invalidate+0x72/0xc0
>> [ 92.277052] __mmu_notifier_invalidate_range_start+0x48/0x60
>> [ 92.277054] migrate_vma_collect+0xf6/0x100
>> [ 92.277055] migrate_vma_setup+0xcf/0x120
>> [ 92.277109] svm_migrate_ram_to_vram+0x256/0x6b0 [amdgpu]
>>
>> 2.Call svm_range_map_to_gpu->amdgpu_vm_update_range to update the page
>> table, at this time it will use the same entry bo which is the want
>> free bo in step1.
>>
>> 3.Then it executes the pt_free_work to free the bo. At this time, the
>> GPU access memory will cause page fault as pt bo has been freed. And
>> then it will call svm_range_restore_pages again.
>>
>> How to fix?
>> Add a workqueue, and flush the workqueue each time before updating page table.
>
>I think this is kind of a known issue in the GPUVM code. Philip was looking at it
>before.
>
>Just flushing a workqueue may seem like a simple and elegant solution, but I'm afraid
>it introduces lock dependency issues. By flushing the workqueue, you're effectively
>creating a lock dependency of the MMU notifier on any locks held inside the worker
>function. You now get a circular lock dependency with any of those locks and memory
>reclaim. I think LOCKDEP would be able to catch that if you compile your kernel with
>that feature enabled.
>
>The proper solution is to prevent delayed freeing of page tables if they happened to
>get reused, or prevent reuse of page tables if they are flagged for delayed freeing.
>
>Regards,
> Felix
>
Thanks, already enabled LOCKDEP while compiling the kernel. The delay work seems for other reasons, I am not sure whether it could be deleted completely.
Emily Deng
Best Wishes
>
>>
>> Signed-off-by: Emily Deng <Emily.Deng@xxxxxxx>
>> ---
>> drivers/gpu/drm/amd/amdgpu/amdgpu.h | 1 +
>> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 1 +
>> drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 7 +++++--
>> drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 6 +++++-
>> drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 3 +++
>> 5 files changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> index 93c352b08969..cbf68ad1c8d0 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>> @@ -1188,6 +1188,7 @@ struct amdgpu_device {
>> struct mutex enforce_isolation_mutex;
>>
>> struct amdgpu_init_level *init_lvl;
>> + struct workqueue_struct *wq;
>> };
>>
>> static inline uint32_t amdgpu_ip_version(const struct amdgpu_device
>> *adev, diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> index f30548f4c3b3..5b4835bc81b3 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> @@ -2069,6 +2069,7 @@ int amdgpu_amdkfd_gpuvm_map_memory_to_gpu(
>> if (ret)
>> goto out;
>> }
>> + flush_workqueue(adev->wq);
>>
>> ret = reserve_bo_and_vm(mem, avm, &ctx);
>> if (unlikely(ret))
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> index 9d6ffe38b48a..500d97cd9114 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> @@ -2607,7 +2607,7 @@ void amdgpu_vm_fini(struct amdgpu_device *adev,
>struct amdgpu_vm *vm)
>> amdgpu_amdkfd_gpuvm_destroy_cb(adev, vm);
>>
>> flush_work(&vm->pt_free_work);
>> -
>> + cancel_work_sync(&vm->pt_free_work);
>> root = amdgpu_bo_ref(vm->root.bo);
>> amdgpu_bo_reserve(root, true);
>> amdgpu_vm_put_task_info(vm->task_info);
>> @@ -2708,6 +2708,8 @@ void amdgpu_vm_manager_init(struct amdgpu_device
>*adev)
>> #endif
>>
>> xa_init_flags(&adev->vm_manager.pasids, XA_FLAGS_LOCK_IRQ);
>> + adev->wq = alloc_workqueue("amdgpu_recycle",
>> + WQ_MEM_RECLAIM | WQ_HIGHPRI |
>WQ_UNBOUND, 16);
>> }
>>
>> /**
>> @@ -2721,7 +2723,8 @@ void amdgpu_vm_manager_fini(struct amdgpu_device
>*adev)
>> {
>> WARN_ON(!xa_empty(&adev->vm_manager.pasids));
>> xa_destroy(&adev->vm_manager.pasids);
>> -
>> + flush_workqueue(adev->wq);
>> + destroy_workqueue(adev->wq);
>> amdgpu_vmid_mgr_fini(adev);
>> }
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
>> index f78a0434a48f..1204406215ee 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
>> @@ -554,15 +554,19 @@ void amdgpu_vm_pt_free_work(struct work_struct
>> *work)
>>
>> vm = container_of(work, struct amdgpu_vm, pt_free_work);
>>
>> + printk("Emily:%s\n", __func__);
>> spin_lock(&vm->status_lock);
>> list_splice_init(&vm->pt_freed, &pt_freed);
>> spin_unlock(&vm->status_lock);
>> + printk("Emily:%s 1\n", __func__);
>>
>> /* flush_work in amdgpu_vm_fini ensure vm->root.bo is valid. */
>> amdgpu_bo_reserve(vm->root.bo, true);
>> + printk("Emily:%s 2\n", __func__);
>>
>> list_for_each_entry_safe(entry, next, &pt_freed, vm_status)
>> amdgpu_vm_pt_free(entry);
>> + printk("Emily:%s 3\n", __func__);
>>
>> amdgpu_bo_unreserve(vm->root.bo);
>> }
>> @@ -589,7 +593,7 @@ void amdgpu_vm_pt_free_list(struct amdgpu_device
>*adev,
>> spin_lock(&vm->status_lock);
>> list_splice_init(¶ms->tlb_flush_waitlist, &vm->pt_freed);
>> spin_unlock(&vm->status_lock);
>> - schedule_work(&vm->pt_free_work);
>> + queue_work(adev->wq, &vm->pt_free_work);
>> return;
>> }
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> index 3e2911895c74..55edf96d5a95 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> @@ -1314,6 +1314,7 @@ svm_range_unmap_from_gpu(struct amdgpu_device
>*adev, struct amdgpu_vm *vm,
>> uint64_t init_pte_value = 0;
>>
>> pr_debug("[0x%llx 0x%llx]\n", start, last);
>> + flush_workqueue(adev->wq);
>>
>> return amdgpu_vm_update_range(adev, vm, false, true, true, false, NULL,
>start,
>> last, init_pte_value, 0, 0, NULL, NULL, @@ -1422,6
>+1423,8
>> @@ svm_range_map_to_gpu(struct kfd_process_device *pdd, struct svm_range
>*prange,
>> * different memory partition based on fpfn/lpfn, we should use
>> * same vm_manager.vram_base_offset regardless memory partition.
>> */
>> + flush_workqueue(adev->wq);
>> +
>> r = amdgpu_vm_update_range(adev, vm, false, false, flush_tlb, true,
>> NULL, last_start, prange->start + i,
>> pte_flags,
