On 26/10/15 13:10, Tvrtko Ursulin wrote:
On 26/10/15 12:10, Chris Wilson wrote:
On Mon, Oct 26, 2015 at 12:00:06PM +0000, Tvrtko Ursulin wrote:
On 26/10/15 11:23, Chris Wilson wrote:
On Mon, Oct 26, 2015 at 11:05:03AM +0000, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
In the following commit:
commit e9f24d5fb7cf3628b195b18ff3ac4e37937ceeae
Author: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Date: Mon Oct 5 13:26:36 2015 +0100
drm/i915: Clean up associated VMAs on context destruction
I added a WARN_ON assertion that VM's active list must be empty
at the time of owning context is getting freed, but that turned
out to be a wrong assumption.
Due ordering of operations in i915_gem_object_retire__read, where
contexts are unreferenced before VMAs are moved to the inactive
list, the described situation can in fact happen.
The context is being unreferenced indirectly. Adding a direct reference
here is even more bizarre.
Perhaps is not the prettiest, but it sounds logical to me to ensure
that order of destruction of involved object hierarchy goes from the
bottom-up and is not interleaved.
If you consider the active/inactive list position as part of the
retire process, doing it at the very place in code, and the very
object that looked to be destroyed out of sequence, to me sounded
logical.
How would you do it, can you think of a better way?
The reference is via the request. We are handling requests, it makes
more sense that you take the reference on the request.
Hm, so you would be happy with:
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 9b2048c7077d..c238481a8090 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2373,19 +2373,26 @@ static void
i915_gem_object_retire__read(struct drm_i915_gem_object *obj, int ring)
{
struct i915_vma *vma;
+ struct drm_i915_gem_request *req;
RQ_BUG_ON(obj->last_read_req[ring] == NULL);
RQ_BUG_ON(!(obj->active & (1 << ring)));
list_del_init(&obj->ring_list[ring]);
+
+ /* Ensure context cannot be destroyed with VMAs on the active list. */
+ req = i915_gem_request_reference(obj->last_read_req[ring]);
+
i915_gem_request_assign(&obj->last_read_req[ring], NULL);
if (obj->last_write_req && obj->last_write_req->ring->id == ring)
i915_gem_object_retire__write(obj);
obj->active &= ~(1 << ring);
- if (obj->active)
+ if (obj->active) {
+ i915_gem_request_unreference(req);
return;
+ }
/* Bump our place on the bound list to keep it roughly in LRU order
* so that we don't steal from recently used but inactive objects
@@ -2399,6 +2406,8 @@ i915_gem_object_retire__read(struct drm_i915_gem_object *obj, int ring)
list_move_tail(&vma->mm_list, &vma->vm->inactive_list);
}
+ i915_gem_request_unreference(req);
+
i915_gem_request_assign(&obj->last_fenced_req, NULL);
drm_gem_object_unreference(&obj->base);
}
Ping on this?
Regards,
Tvrtko
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