dma-buf: Report signaled links inside dma-fence-chain

Whenever we walk along the dma-fence-chain, we prune signaled links to
keep the chain nice and tidy. This leads to situations where we can
prune a link and report the earlier fence as the target seqno --
violating our own consistency checks that the seqno is not more advanced
than the last element in a dma-fence-chain.

Report a NULL fence and success if the seqno has already been signaled.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
Reviewed-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200409110101.18400-2-chris@chris-wilson.co.uk

diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c
index 3d12350..c435bbb 100644 (file)
--- a/drivers/dma-buf/dma-fence-chain.c
+++ b/drivers/dma-buf/dma-fence-chain.c
@@ -99,6 +99,12 @@ int dma_fence_chain_find_seqno(struct dma_fence **pfence, uint64_t seqno)
                return -EINVAL;
 
        dma_fence_chain_for_each(*pfence, &chain->base) {
+               if ((*pfence)->seqno < seqno) { /* already signaled */
+                       dma_fence_put(*pfence);
+                       *pfence = NULL;
+                       break;
+               }
+
                if ((*pfence)->context != chain->base.context ||
                    to_dma_fence_chain(*pfence)->prev_seqno < seqno)
                        break;
@@ -222,6 +228,7 @@ EXPORT_SYMBOL(dma_fence_chain_ops);
  * @chain: the chain node to initialize
  * @prev: the previous fence
  * @fence: the current fence
+ * @seqno: the sequence number (syncpt) of the fence within the chain
  *
  * Initialize a new chain node and either start a new chain or add the node to
  * the existing chain of the previous fence.