DAOS-16211 vos: Avoid race condition with discard (#15370)

There is a possible race between aggregation deleting
the object tree and discard working on the same
object tree.  Add a check to avoid this race

Signed-off-by: Jeff Olivier <jeffolivier@google.com>

src/vos/vos_obj_index.c

@@ -793,6 +793,7 @@ oi_iter_check_punch(daos_handle_t ih)
 {
 	struct vos_iterator	*iter = vos_hdl2iter(ih);
 	struct vos_oi_iter	*oiter = iter2oiter(iter);
+	struct vos_container	*cont  = oiter->oit_cont;
 	struct vos_obj_df	*obj;
 	struct oi_delete_arg	del_arg;
 	daos_unit_oid_t		 oid;
@@ -811,10 +812,22 @@ oi_iter_check_punch(daos_handle_t ih)
 	obj = (struct vos_obj_df *)rec_iov.iov_buf;
 	oid = obj->vo_id;
 
-	if (!vos_ilog_is_punched(vos_cont2hdl(oiter->oit_cont), &obj->vo_ilog, &oiter->oit_epr,
-				 NULL, &oiter->oit_ilog_info))
+	if (!vos_ilog_is_punched(vos_cont2hdl(cont), &obj->vo_ilog, &oiter->oit_epr, NULL,
+				 &oiter->oit_ilog_info))
 		return 0;
 
+	rc = vos_obj_hold(vos_obj_cache_current(cont->vc_pool->vp_sysdb), cont, oid,
+			  &oiter->oit_epr, iter->it_bound, VOS_OBJ_AGGREGATE | VOS_OBJ_NO_HOLD,
+			  DAOS_INTENT_PURGE, NULL, NULL);
+	if (rc != 0) {
+		/** -DER_BUSY means the object is in-use already.  We will after a yield in this
+		 * case.
+		 */
+		D_CDEBUG(rc == -DER_BUSY, DB_EPC, DLOG_ERR, "Hold check failed for " DF_UOID "\n",
+			 DP_UOID(oid));
+		return rc;
+	}
+
 	/** Ok, ilog is fully punched, so we can move it to gc heap */
 	rc = umem_tx_begin(vos_cont2umm(oiter->oit_cont), NULL);
 	if (rc != 0)