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