On Fri 2022-02-25 11:15 +0100, Petr Mladek wrote: > rcu_dereference_sched() makes sparse happy. But lockdep complains > because the _rcu pointer is not accessed under: > > rcu_read_lock_sched(); > rcu_read_unlock_sched(); Hi Petr, > > This is not the case here. Note that module_mutex does not > disable preemtion. > > Now, the code is safe. The RCU access makes sure that "mod" > can't be freed in the meantime: > > + add_kallsyms() is called by the module loaded when the module > is being loaded. It could not get removed in parallel > by definition. > > + module_kallsyms_on_each_symbol() takes module_mutex. > It means that the module could not get removed. Indeed, which is why I did not use rcu_read_lock_sched() and rcu_read_unlock_sched() with rcu_dereference_sched(). That being said, I should have mentioned this in the commit message. > IMHO, we have two possibilities here: > > + Make sparse and lockdep happy by using rcu_dereference_sched() > and calling the code under rcu_read_lock_sched(). > > + Cast (struct mod_kallsyms *)mod->kallsyms when accessing > the value. I prefer the first option. > I do not have strong preference. I am fine with both. > > Anyway, such a fix should be done in a separate patch! Agreed. Kind regards, -- Aaron Tomlin
