drm/ttm: Fix up a theoretical deadlock (95ccb0f3) · Commits · e / devices / android_kernel_fairphone_FP5

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> Signed-off-by:

Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ttm/ttm_bo.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -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 {