Hi, Christian,
While this has probably already been committed, and looks like a nice
cleanup there are two things below I think needs fixing.
On 11/15/2017 01:31 PM, Christian König wrote:
There is no guarantee that the next entry on the ddelete list stays on
the list when we drop the locks.
Completely rework this mess by moving processed entries on a temporary
list.
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
drivers/gpu/drm/ttm/ttm_bo.c | 77 ++++++++++++++------------------------------
1 file changed, 25 insertions(+), 52 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 7c1eac4f4b4b..ad0afdd71f21 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -572,71 +572,47 @@ static int ttm_bo_cleanup_refs(struct ttm_buffer_object *bo,
* Traverse the delayed list, and call ttm_bo_cleanup_refs on all
* encountered buffers.
*/
-
-static int ttm_bo_delayed_delete(struct ttm_bo_device *bdev, bool remove_all)
+static bool ttm_bo_delayed_delete(struct ttm_bo_device *bdev, bool remove_all)
{
struct ttm_bo_global *glob = bdev->glob;
- struct ttm_buffer_object *entry = NULL;
- int ret = 0;
-
- spin_lock(&glob->lru_lock);
- if (list_empty(&bdev->ddestroy))
- goto out_unlock;
+ struct list_head removed;
+ bool empty;
- entry = list_first_entry(&bdev->ddestroy,
- struct ttm_buffer_object, ddestroy);
- kref_get(&entry->list_kref);
+ INIT_LIST_HEAD(&removed);
- for (;;) {
- struct ttm_buffer_object *nentry = NULL;
-
- if (entry->ddestroy.next != &bdev->ddestroy) {
- nentry = list_first_entry(&entry->ddestroy,
- struct ttm_buffer_object, ddestroy);
- kref_get(&nentry->list_kref);
- }
-
- ret = reservation_object_trylock(entry->resv) ? 0 : -EBUSY;
- if (remove_all && ret) {
- spin_unlock(&glob->lru_lock);
- ret = reservation_object_lock(entry->resv, NULL);
- spin_lock(&glob->lru_lock);
- }
+ spin_lock(&glob->lru_lock);
+ while (!list_empty(&bdev->ddestroy)) {
+ struct ttm_buffer_object *bo;
- if (!ret)
- ret = ttm_bo_cleanup_refs(entry, false, !remove_all,
- true);
- else
- spin_unlock(&glob->lru_lock);
+ bo = list_first_entry(&bdev->ddestroy, struct ttm_buffer_object,
+ ddestroy);
+ kref_get(&bo->list_kref);
+ list_move_tail(&bo->ddestroy, &removed);
+ spin_unlock(&glob->lru_lock);
- kref_put(&entry->list_kref, ttm_bo_release_list);
- entry = nentry;
+ reservation_object_lock(bo->resv, NULL);
Reservation may be a long lived lock, and typically if the object is
reserved here, it's being evicted somewhere and there might be a
substantial stall, which isn't really acceptable in the global
workqueue. Better to move on to the next bo.
This function was really intended to be non-blocking, unless remove_all
== true. I even think it's safe to keep the spinlock held on tryreserve?
- if (ret || !entry)
- goto out;
+ spin_lock(&glob->lru_lock);
+ ttm_bo_cleanup_refs(bo, false, !remove_all, true);
+ kref_put(&bo->list_kref, ttm_bo_release_list);
Calling a release function in atomic context is a bad thing. Nobody
knows what locks needs to be taken in the release function and such code
is prone to lock inversion and sleep-while-atomic bugs. Not long ago
vfree() was even forbidden from atomic context. But here it's easily
avoidable.
/Thomas
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