On Wed, Mar 02, 2022 at 11:21:59AM +0100, Thomas Hellström wrote:
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.
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_gem.c | 17 +++++++++++++----
drivers/gpu/drm/i915/i915_vma.c | 14 +++-----------
drivers/gpu/drm/i915/i915_vma.h | 14 --------------
drivers/gpu/drm/i915/i915_vma_types.h | 1 -
4 files changed, 16 insertions(+), 30 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index dd84ebabb50f..c26110abcc0b 100644
--- 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);
One issue still left in i915_gem_object_unbind is that it temporarily removes
vmas from the obj->vma.list and adds back later as vma needs to be unbind outside
the obj->vma.lock spinlock. This is an issue for other places where we iterate
over the obj->vma.list. i915_debugfs_describe_obj is one such case (upcoming
vm_bind will be another) that iterates over this list.
What is the plan here? Do we need to take object lock while iterating over the
list?
But this just something I noticed and not related to this patch.
This patch looks good to me.
Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@xxxxxxxxx>
diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 91538bc38110..6fd25b39748f 100644
--- 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);
}
/**
diff --git a/drivers/gpu/drm/i915/i915_vma.h b/drivers/gpu/drm/i915/i915_vma.h
index 67ae7341c7e0..6034991d89fe 100644
--- 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
index eac36be184e5..be6e028c3b57 100644
--- 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;
/**
--
2.34.1
