Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules
From: Joel Fernandes
Date: Tue Apr 02 2019 - 14:41:01 EST
On Tue, Apr 02, 2019 at 08:23:34AM -0700, Paul E. McKenney wrote:
> On Tue, Apr 02, 2019 at 11:14:40AM -0400, Mathieu Desnoyers wrote:
> > ----- On Apr 2, 2019, at 10:28 AM, paulmck paulmck@xxxxxxxxxxxxx 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?
Which 'reserved region' are you referring to? Isn't this region also
used for non-module cases in which case the same problem applies to