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[Oleg Bondarev <obondarev@xxxxxxxxxxxx>]

Public bug reported:

wrapped_db_retry may not work as expected if wrapped function modifies
it's mutable arguments during execution: in this case on the second
attempt the function will be called with modified args. Example:

    def create_router(self, context, router):
        r = router['router']
        gw_info = r.pop(EXTERNAL_GW_INFO, None)
        tenant_id = self._get_tenant_id_for_create(context, r)
        with context.session.begin(subtransactions=True):
            router_db = self._create_router_db(context, r, tenant_id)
            if gw_info:
                self._update_router_gw_info(context, router_db['id'],
                                            gw_info, router=router_db)
        dict =  self._make_router_dict(router_db)
        return dict

because of pop() on a second attempt the router dict will not have
gateway info so router will be created without it, silently and
surprisingly for users.

Just doing copy.deepcopy() inside wrap_db_retry will not work as
arguments might be complex objects(like plugins) which do not support
deepcopy(). So this needs a more crafty fix. Otherwise wrap_db_retry
should be used carefully, checking that wrapped function does not modify
mutable args.

Currently neutron uses wrap_db_retry at API layer which is not safe
given described issue.

** Affects: neutron
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1480319

Title:
  Mutable args and wrap_db_retry

Status in neutron:
  New

Bug description:
  wrapped_db_retry may not work as expected if wrapped function modifies
  it's mutable arguments during execution: in this case on the second
  attempt the function will be called with modified args. Example:

      def create_router(self, context, router):
          r = router['router']
          gw_info = r.pop(EXTERNAL_GW_INFO, None)
          tenant_id = self._get_tenant_id_for_create(context, r)
          with context.session.begin(subtransactions=True):
              router_db = self._create_router_db(context, r, tenant_id)
              if gw_info:
                  self._update_router_gw_info(context, router_db['id'],
                                              gw_info, router=router_db)
          dict =  self._make_router_dict(router_db)
          return dict

  because of pop() on a second attempt the router dict will not have
  gateway info so router will be created without it, silently and
  surprisingly for users.

  Just doing copy.deepcopy() inside wrap_db_retry will not work as
  arguments might be complex objects(like plugins) which do not support
  deepcopy(). So this needs a more crafty fix. Otherwise wrap_db_retry
  should be used carefully, checking that wrapped function does not
  modify mutable args.

  Currently neutron uses wrap_db_retry at API layer which is not safe
  given described issue.

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