On 11/28/2012 12:25 PM, Maarten Lankhorst wrote:
> This requires changing the order in ttm_bo_cleanup_refs_or_queue to
> take the reservation first, as there is otherwise no race free way to
> take lru lock before fence_lock.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at canonical.com>
Technically I think it would be possible to avoid reserving in the case
the bo is still busy, and re-checking
for sync_obj presence once we have reserved (since we release the fence
lock).
But that's an optimization. The important thing at this point is to get
this right.
Reviewed-by: Thomas Hellstrom <thellstrom at vmware.com>
> ---
> drivers/gpu/drm/ttm/ttm_bo.c | 31 +++++++++++--------------------
> drivers/gpu/drm/ttm/ttm_execbuf_util.c | 4 ++--
> 2 files changed, 13 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index 7426fe5..202fc20 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -500,27 +500,17 @@ static void ttm_bo_cleanup_refs_or_queue(struct
> ttm_buffer_object *bo)
> {
> struct ttm_bo_device *bdev = bo->bdev;
> struct ttm_bo_global *glob = bo->glob;
> - struct ttm_bo_driver *driver;
> + struct ttm_bo_driver *driver = bdev->driver;
> void *sync_obj = NULL;
> int put_count;
> int ret;
>
> + spin_lock(&glob->lru_lock);
> + ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
> +
> spin_lock(&bdev->fence_lock);
> (void) ttm_bo_wait(bo, false, false, true);
> - if (!bo->sync_obj) {
> -
> - spin_lock(&glob->lru_lock);
> -
> - /**
> - * Lock inversion between bo:reserve and bdev::fence_lock here,
> - * but that's OK, since we're only trylocking.
> - */
> -
> - ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
> -
> - if (unlikely(ret == -EBUSY))
> - goto queue;
> -
> + if (!ret && !bo->sync_obj) {
> spin_unlock(&bdev->fence_lock);
> put_count = ttm_bo_del_from_lru(bo);
>
> @@ -530,18 +520,19 @@ static void ttm_bo_cleanup_refs_or_queue(struct
> ttm_buffer_object *bo)
> ttm_bo_list_ref_sub(bo, put_count, true);
>
> return;
> - } else {
> - spin_lock(&glob->lru_lock);
> }
> -queue:
> - driver = bdev->driver;
> if (bo->sync_obj)
> sync_obj = driver->sync_obj_ref(bo->sync_obj);
> + spin_unlock(&bdev->fence_lock);
> +
> + if (!ret) {
> + atomic_set(&bo->reserved, 0);
> + wake_up_all(&bo->event_queue);
> + }
>
> kref_get(&bo->list_kref);
> list_add_tail(&bo->ddestroy, &bdev->ddestroy);
> spin_unlock(&glob->lru_lock);
> - spin_unlock(&bdev->fence_lock);
>
> if (sync_obj) {
> driver->sync_obj_flush(sync_obj);
> diff --git a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
> b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
> index 1986d00..cd9e452 100644
> --- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
> @@ -213,8 +213,8 @@ void ttm_eu_fence_buffer_objects(struct list_head *list,
> void *sync_obj)
> driver = bdev->driver;
> glob = bo->glob;
>
> - spin_lock(&bdev->fence_lock);
> spin_lock(&glob->lru_lock);
> + spin_lock(&bdev->fence_lock);
>
> list_for_each_entry(entry, list, head) {
> bo = entry->bo;
> @@ -223,8 +223,8 @@ void ttm_eu_fence_buffer_objects(struct list_head *list,
> void *sync_obj)
> ttm_bo_unreserve_locked(bo);
> entry->reserved = false;
> }
> - spin_unlock(&glob->lru_lock);
> spin_unlock(&bdev->fence_lock);
> + spin_unlock(&glob->lru_lock);
>
> list_for_each_entry(entry, list, head) {
> if (entry->old_sync_obj)
