On Mon, 1 Feb 2021, Jessica Yu wrote: > +++ Miroslav Benes [29/01/21 16:29 +0100]: > >On Thu, 28 Jan 2021, Christoph Hellwig wrote: > > > >> Allow for a RCU-sched critical section around find_module, following > >> the lower level find_module_all helper, and switch the two callers > >> outside of module.c to use such a RCU-sched critical section instead > >> of module_mutex. > > > >That's a nice idea. > > > >> @@ -57,7 +58,7 @@ static void klp_find_object_module(struct klp_object > >> *obj) > >> if (!klp_is_module(obj)) > >> return; > >> > >> - mutex_lock(&module_mutex); > >> + rcu_read_lock_sched(); > >> /* > >> * We do not want to block removal of patched modules and therefore > >> * we do not take a reference here. The patches are removed by > >> @@ -74,7 +75,7 @@ static void klp_find_object_module(struct klp_object > >> *obj) > >> if (mod && mod->klp_alive) > > > >RCU always baffles me a bit, so I'll ask. Don't we need > >rcu_dereference_sched() here? "mod" comes from a RCU-protected list, so I > >wonder. > > Same here :-) I had to double check the RCU documentation. For our > modules list case I believe the rcu list API should take care of that > for us. Worth noting is this snippet from Documentation/RCU/whatisRCU.txt: > > rcu_dereference() is typically used indirectly, via the _rcu > list-manipulation primitives, such as list_for_each_entry_rcu() Ok, thanks to both for checking and explanation. Ack to the patch then. Miroslav
