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

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Message-Id: <20181112163139.GN4170@linux.ibm.com>
Date:   Mon, 12 Nov 2018 08:31:39 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Jessica Yu <jeyu@...nel.org>
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()

On Mon, Nov 12, 2018 at 01:48:52PM +0100, Jessica Yu wrote:
> +++ 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>

Applied, thank you!

							Thanx, Paul

> 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
> >
>