Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules

On Tue, Apr 02, 2019 at 11:14:40AM -0400, Mathieu Desnoyers wrote: > ----- On Apr 2, 2019, at 10:28 AM, paulmck paulmck(a)linux.ibm.com wrote: > > > Hello! > > > > This series prohibits use of DEFINE_SRCU() and DEFINE_STATIC_SRCU() > > by loadable modules. The reason for this prohibition is the fact > > that using these two macros within modules requires that the size of > > the reserved region be increased, which is not something we want to > > be doing all that often. Instead, loadable modules should define an > > srcu_struct and invoke init_srcu_struct() from their module_init function > > and cleanup_srcu_struct() from their module_exit function. Note that > > modules using call_srcu() will also need to invoke srcu_barrier() from > > their module_exit function. > > This arbitrary API limitation seems weird. > > Isn't there a way to allow modules to use DEFINE_SRCU and DEFINE_STATIC_SRCU > while implementing them with dynamic allocation under the hood ? Although call_srcu() already has initialization hooks, some would also be required in srcu_read_lock(), and I am concerned about adding memory allocation at that point, especially given the possibility of memory-allocation failure. And the possibility that the first srcu_read_lock() happens in an interrupt handler or similar. Or am I missing a trick here?