Re: [PATCH tip/core/rcu 24/41] modules: Replace synchronize_sched() and call_rcu_sched()

[Jessica Yu]

+++ Paul E. McKenney [11/11/18 11:43 -0800]:
> Now that synchronize_rcu() waits for preempt-disable regions of code
> as well as RCU read-side critical sections, synchronize_sched() can
> be replaced by synchronize_rcu().  Similarly, call_rcu_sched() can be
> replaced by call_rcu().  This commit therefore makes these changes.
>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
> Cc: Jessica Yu <jeyu@xxxxxxxxxx>

Acked-by: Jessica Yu <jeyu@xxxxxxxxxx>

Thanks!

> ---
> kernel/module.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 49a405891587..99b46c32d579 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2159,7 +2159,7 @@ static void free_module(struct module *mod)
> 	/* Remove this module from bug list, this uses list_del_rcu */
> 	module_bug_cleanup(mod);
> 	/* Wait for RCU-sched synchronizing before releasing mod->list and buglist. */
> -	synchronize_sched();
> +	synchronize_rcu();
> 	mutex_unlock(&module_mutex);
>
> 	/* This may be empty, but that's OK */
> @@ -3507,15 +3507,15 @@ static noinline int do_init_module(struct module *mod)
> 	/*
> 	 * We want to free module_init, but be aware that kallsyms may be
> 	 * walking this with preempt disabled.  In all the failure paths, we
> -	 * call synchronize_sched(), but we don't want to slow down the success
> +	 * call synchronize_rcu(), but we don't want to slow down the success
> 	 * path, so use actual RCU here.
> 	 * Note that module_alloc() on most architectures creates W+X page
> 	 * mappings which won't be cleaned up until do_free_init() runs.  Any
> 	 * code such as mark_rodata_ro() which depends on those mappings to
> 	 * be cleaned up needs to sync with the queued work - ie
> -	 * rcu_barrier_sched()
> +	 * rcu_barrier()
> 	 */
> -	call_rcu_sched(&freeinit->rcu, do_free_init);
> +	call_rcu(&freeinit->rcu, do_free_init);
> 	mutex_unlock(&module_mutex);
> 	wake_up_all(&module_wq);
>
> @@ -3526,7 +3526,7 @@ static noinline int do_init_module(struct module *mod)
> fail:
> 	/* Try to protect us from buggy refcounters. */
> 	mod->state = MODULE_STATE_GOING;
> -	synchronize_sched();
> +	synchronize_rcu();
> 	module_put(mod);
> 	blocking_notifier_call_chain(&module_notify_list,
> 				     MODULE_STATE_GOING, mod);
> @@ -3819,7 +3819,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
>  ddebug_cleanup:
> 	ftrace_release_mod(mod);
> 	dynamic_debug_remove(mod, info->debug);
> -	synchronize_sched();
> +	synchronize_rcu();
> 	kfree(mod->args);
>  free_arch_cleanup:
> 	module_arch_cleanup(mod);
> @@ -3834,7 +3834,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
> 	mod_tree_remove(mod);
> 	wake_up_all(&module_wq);
> 	/* Wait for RCU-sched synchronizing before releasing mod->list. */
> -	synchronize_sched();
> +	synchronize_rcu();
> 	mutex_unlock(&module_mutex);
>  free_module:
> 	/* Free lock-classes; relies on the preceding sync_rcu() */
> --
> 2.17.1