linux-kernel - Re: [PATCH tip/core/rcu 24/41] modules: Replace synchronize_sched() and call_rcu

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Date:   Mon, 12 Nov 2018 13:48:52 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org
Subject: Re: [PATCH tip/core/rcu 24/41] modules: Replace synchronize_sched()
 and call_rcu_sched()

+++ 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@...ux.ibm.com>
>Cc: Jessica Yu <jeyu@...nel.org>

Acked-by: Jessica Yu <jeyu@...nel.org>

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
>