A process suspended waiting for a higher sequence or no sequence to unreserve, a bo may be beaten to the reservation by a process with a lower sequence. In that case the first process should give up trying to reserve and return -EAGAIN. In order for that to happen, we must wake waiting processes when we change sequence, so that they have a chance to detect the new sequence.
Signed-off-by: Thomas Hellstrom thellstrom@vmware.com --- drivers/gpu/drm/ttm/ttm_bo.c | 11 +++++++++++ 1 files changed, 11 insertions(+), 0 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c index 3ca77dc..148a322 100644 --- a/drivers/gpu/drm/ttm/ttm_bo.c +++ b/drivers/gpu/drm/ttm/ttm_bo.c @@ -224,6 +224,9 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo, int ret;
while (unlikely(atomic_cmpxchg(&bo->reserved, 0, 1) != 0)) { + /** + * Deadlock avoidance for multi-bo reserving. + */ if (use_sequence && bo->seq_valid && (sequence - bo->val_seq < (1 << 31))) { return -EAGAIN; @@ -241,6 +244,14 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo, }
if (use_sequence) { + /** + * Wake up waiters that may need to recheck for deadlock, + * if we decreased the sequence number. + */ + if (unlikely((bo->val_seq - sequence < (1 << 31)) + || !bo->seq_valid)) + wake_up_all(&bo->event_queue); + bo->val_seq = sequence; bo->seq_valid = true; } else {