Re: [PATCH v5 1/1] drm/amdgpu: Fix amdgpu_vm_pt_free warning

[Christian König]

Am 14.09.22 um 19:45 schrieb Felix Kuehling:
Am 2022-09-14 um 12:08 schrieb Philip Yang:
Free page table BO from vm resv unlocked context generate below
warnings.
Add a pt_free_work in vm to free page table BO from vm->pt_freed list.
pass vm resv unlock status from page table update caller, and add vm_bo
entry to vm->pt_freed list and schedule the pt_free_work if calling with
vm resv unlocked.

WARNING: CPU: 12 PID: 3238 at
drivers/gpu/drm/ttm/ttm_bo.c:106 ttm_bo_set_bulk_move+0xa1/0xc0
Call Trace:
  amdgpu_vm_pt_free+0x42/0xd0 [amdgpu]
  amdgpu_vm_pt_free_dfs+0xb3/0xf0 [amdgpu]
  amdgpu_vm_ptes_update+0x52d/0x850 [amdgpu]
  amdgpu_vm_update_range+0x2a6/0x640 [amdgpu]
  svm_range_unmap_from_gpus+0x110/0x300 [amdgpu]
  svm_range_cpu_invalidate_pagetables+0x535/0x600 [amdgpu]
  __mmu_notifier_invalidate_range_start+0x1cd/0x230
  unmap_vmas+0x9d/0x140
  unmap_region+0xa8/0x110

Signed-off-by: Philip Yang <philip.y...@amd.com>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c    |  5 +++
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h    |  6 ++++
  drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 41 +++++++++++++++++++++--
  3 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index 59cac347baa3..20cfc8c9635b 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -2022,6 +2022,9 @@ int amdgpu_vm_init(struct amdgpu_device *adev, 
struct amdgpu_vm *vm)
      spin_lock_init(&vm->invalidated_lock);
      INIT_LIST_HEAD(&vm->freed);
      INIT_LIST_HEAD(&vm->done);
+    INIT_LIST_HEAD(&vm->pt_freed);
+    INIT_WORK(&vm->pt_free_work, amdgpu_vm_pt_free_work);
+    spin_lock_init(&vm->pt_free_lock);
        /* create scheduler entities for page table updates */
      r = drm_sched_entity_init(&vm->immediate, 
DRM_SCHED_PRIORITY_NORMAL,
@@ -2223,6 +2226,8 @@ 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);
+
      root = amdgpu_bo_ref(vm->root.bo);
      amdgpu_bo_reserve(root, true);
      amdgpu_vm_set_pasid(adev, vm, 0);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
index 9ecb7f663e19..b77fe838c327 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
@@ -276,6 +276,11 @@ struct amdgpu_vm {
      /* BOs which are invalidated, has been updated in the PTs */
      struct list_head        done;
  +    /* PT BOs scheduled to free and fill with zero if vm_resv is 
not hold */
+    struct list_head    pt_freed;
+    struct work_struct    pt_free_work;
+    spinlock_t        pt_free_lock;
+
      /* contains the page directory */
      struct amdgpu_vm_bo_base     root;
      struct dma_fence    *last_update;
@@ -471,6 +476,7 @@ int amdgpu_vm_pde_update(struct 
amdgpu_vm_update_params *params,
  int amdgpu_vm_ptes_update(struct amdgpu_vm_update_params *params,
                uint64_t start, uint64_t end,
                uint64_t dst, uint64_t flags);
+void amdgpu_vm_pt_free_work(struct work_struct *work);
    #if defined(CONFIG_DEBUG_FS)
  void amdgpu_debugfs_vm_bo_info(struct amdgpu_vm *vm, struct 
seq_file *m);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
index 88de9f0d4728..c16579471f22 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
@@ -641,6 +641,27 @@ static void amdgpu_vm_pt_free(struct 
amdgpu_vm_bo_base *entry)
      amdgpu_bo_unref(&entry->bo);
  }
  +void amdgpu_vm_pt_free_work(struct work_struct *work)
+{
+    struct amdgpu_vm_bo_base *entry, *next;
+    struct amdgpu_vm *vm;
+    LIST_HEAD(pt_freed);
+
+    vm = container_of(work, struct amdgpu_vm, pt_free_work);
+
+    spin_lock(&vm->pt_free_lock);
+    list_splice_init(&vm->pt_freed, &pt_freed);
+    spin_unlock(&vm->pt_free_lock);
+
+    // flush_work in amdgpu_vm_fini ensure vm->root.bo is valid
+    amdgpu_bo_reserve(vm->root.bo, true);
+
+    list_for_each_entry_safe(entry, next, &pt_freed, vm_status)
+        amdgpu_vm_pt_free(entry);
+
+    amdgpu_bo_unreserve(vm->root.bo);
+}
+
  /**
   * amdgpu_vm_pt_free_dfs - free PD/PT levels
   *
@@ -652,11 +673,24 @@ static void amdgpu_vm_pt_free(struct 
amdgpu_vm_bo_base *entry)
   */
  static void amdgpu_vm_pt_free_dfs(struct amdgpu_device *adev,
                    struct amdgpu_vm *vm,
-                  struct amdgpu_vm_pt_cursor *start)
+                  struct amdgpu_vm_pt_cursor *start,
+                  bool unlocked)
  {
      struct amdgpu_vm_pt_cursor cursor;
      struct amdgpu_vm_bo_base *entry;
  +    if (unlocked) {
+        spin_lock(&vm->pt_free_lock);
+        for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
+            list_move(&entry->vm_status, &vm->pt_freed);
+
+        if (start)
+            list_move(&start->entry->vm_status, &vm->pt_freed);
+        spin_unlock(&vm->pt_free_lock);

Question for Christian: list_move will take the entry off another 
vm_status list (evicted, idle, invalidated, relocated). I don't think 
this is safe without holding a reservation lock in most cases. Since 
the point here is to maintain a list of PTs to be freed without 
locking a reservation, is the vm_status really the right way to do this?

Oh, good point. This means we need to protect the whole state machine 
with a spinlock or use a separate deleted list.

I don't see how we can easily use a separate list here, but we already 
have the invalidated_lock, maybe we need to rename this one to status 
lock and use it for all cases.

Regards,
Christian.


Regards,
  Felix


+ schedule_work(&vm->pt_free_work);
+        return;
+    }
+
      for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
          amdgpu_vm_pt_free(entry);
  @@ -673,7 +707,7 @@ static void amdgpu_vm_pt_free_dfs(struct 
amdgpu_device *adev,
   */
  void amdgpu_vm_pt_free_root(struct amdgpu_device *adev, struct 
amdgpu_vm *vm)
  {
-    amdgpu_vm_pt_free_dfs(adev, vm, NULL);
+    amdgpu_vm_pt_free_dfs(adev, vm, NULL, false);
  }
    /**
@@ -966,7 +1000,8 @@ int amdgpu_vm_ptes_update(struct 
amdgpu_vm_update_params *params,
                  if (cursor.entry->bo) {
                      params->table_freed = true;
                      amdgpu_vm_pt_free_dfs(adev, params->vm,
-                                  &cursor);
+                                  &cursor,
+                                  params->unlocked);
                  }
                  amdgpu_vm_pt_next(adev, &cursor);
              }