drm/i915: Remove the vma refcount

Now that i915_vma_parked() is taking the object lock on vma destruction, and the only user of the vma refcount, i915_gem_object_unbind() also takes the object lock, remove the vma refcount. v3: Documentation update. Signed-off-by: Thomas Hellström <[email protected]> Reviewed-by: Niranjana Vishwanathapura <[email protected]> Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
torvalds · Mar 7, 2022 · d939397 · d939397
1 parent e1a7ab4
commit d939397
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Showing 4 changed files with 16 additions and 33 deletions.
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
@@ -151,14 +151,25 @@ int i915_gem_object_unbind(struct drm_i915_gem_object *obj,
  break;
  }
 
+ /*
+ * Requiring the vm destructor to take the object lock
+ * before destroying a vma would help us eliminate the
+ * i915_vm_tryget() here, AND thus also the barrier stuff
+ * at the end. That's an easy fix, but sleeping locks in
+ * a kthread should generally be avoided.
+ */
  ret = -EAGAIN;
  if (!i915_vm_tryget(vma->vm))
  break;
 
- /* Prevent vma being freed by i915_vma_parked as we unbind */
- vma = __i915_vma_get(vma);
  spin_unlock(&obj->vma.lock);
 
+ /*
+ * Since i915_vma_parked() takes the object lock
+ * before vma destruction, it won't race us here,
+ * and destroy the vma from under us.
+ */
+
  if (vma) {
  bool vm_trylock = !!(flags & I915_GEM_OBJECT_UNBIND_VM_TRYLOCK);
  ret = -EBUSY;
@@ -180,8 +191,6 @@ int i915_gem_object_unbind(struct drm_i915_gem_object *obj,
  ret = i915_vma_unbind(vma);
  }
  }
-
- __i915_vma_put(vma);
  }
 
  i915_vm_put(vma->vm);

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
@@ -122,7 +122,6 @@ vma_create(struct drm_i915_gem_object *obj,
  if (vma == NULL)
  return ERR_PTR(-ENOMEM);
 
- kref_init(&vma->ref);
  vma->ops = &vm->vma_ops;
  vma->obj = obj;
  vma->size = obj->base.size;
@@ -1628,15 +1627,6 @@ void i915_vma_reopen(struct i915_vma *vma)
  __i915_vma_remove_closed(vma);
 }
 
-void i915_vma_release(struct kref *ref)
-{
- struct i915_vma *vma = container_of(ref, typeof(*vma), ref);
-
- i915_active_fini(&vma->active);
- GEM_WARN_ON(vma->resource);
- i915_vma_free(vma);
-}
-
 static void force_unbind(struct i915_vma *vma)
 {
  if (!drm_mm_node_allocated(&vma->node))
@@ -1665,7 +1655,9 @@ static void release_references(struct i915_vma *vma, bool vm_ddestroy)
  if (vm_ddestroy)
  i915_vm_resv_put(vma->vm);
 
- __i915_vma_put(vma);
+ i915_active_fini(&vma->active);
+ GEM_WARN_ON(vma->resource);
+ i915_vma_free(vma);
 }
 
 /**
@@ -1693,9 +1685,6 @@ static void release_references(struct i915_vma *vma, bool vm_ddestroy)
  * - vm->mutex
  * - obj->vma.lock
  * - gt->closed_lock
- *
- * A vma user can also temporarily keep the vma alive while holding a vma
- * reference.
  */
 void i915_vma_destroy_locked(struct i915_vma *vma)
 {

diff --git a/drivers/gpu/drm/i915/i915_vma.h b/drivers/gpu/drm/i915/i915_vma.h
@@ -222,20 +222,6 @@ void i915_vma_unlink_ctx(struct i915_vma *vma);
 void i915_vma_close(struct i915_vma *vma);
 void i915_vma_reopen(struct i915_vma *vma);
 
-static inline struct i915_vma *__i915_vma_get(struct i915_vma *vma)
-{
- if (kref_get_unless_zero(&vma->ref))
- return vma;
-
- return NULL;
-}
-
-void i915_vma_release(struct kref *ref);
-static inline void __i915_vma_put(struct i915_vma *vma)
-{
- kref_put(&vma->ref, i915_vma_release);
-}
-
 void i915_vma_destroy_locked(struct i915_vma *vma);
 void i915_vma_destroy(struct i915_vma *vma);
 

diff --git a/drivers/gpu/drm/i915/i915_vma_types.h b/drivers/gpu/drm/i915/i915_vma_types.h
@@ -211,7 +211,6 @@ struct i915_vma {
  * handles (but same file) for execbuf, i.e. the number of aliases
  * that exist in the ctx->handle_vmas LUT for this vma.
  */
- struct kref ref;
  atomic_t open_count;
  atomic_t flags;
  /**