Bluetooth: Controller: Fix advertising pdu latest get

Fix advertising pdu latest get to defer release of stale
PDU chain buffers. Returning NULL after some buffers where
released causes LLL to assert when chained PDUs are
switched.

Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: cvinayak

subsys/bluetooth/controller/ll_sw/nordic/lll/lll_adv.c

@@ -472,8 +472,7 @@ struct pdu_adv *lll_adv_pdu_latest_get(struct lll_adv_pdu *pdu,
 			 * switch attempt (on next event).
 			 */
 			if (!MFIFO_ENQUEUE_IDX_GET(pdu_free, &free_idx)) {
-				pdu->pdu[pdu_idx] = p;
-				return NULL;
+				break;
 			}
 
 #if defined(CONFIG_BT_CTLR_ADV_PDU_LINK)
@@ -488,16 +487,19 @@ struct pdu_adv *lll_adv_pdu_latest_get(struct lll_adv_pdu *pdu,
 			p = next;
 		} while (p);
 
-		pdu->pdu[pdu_idx] = NULL;
+		/* If not all PDUs where released into mfifo, keep the list in
+		 * current data index, to be released on the next switch
+		 * attempt.
+		 */
+		pdu->pdu[pdu_idx] = p;
 
+		/* Progress to next data index */
 		first += 1U;
 		if (first == DOUBLE_BUFFER_SIZE) {
 			first = 0U;
 		}
 		pdu->first = first;
 		*is_modified = 1U;
-
-		pdu->pdu[pdu_idx] = NULL;
 	}
 
 	return (void *)pdu->pdu[first];