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 at 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 {
--
1.6.2.5
