linux-kernel - [PATCH 13/18] rcu: Assume rcu_report

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Message-Id: <20231013115902.1059735-14-frederic@kernel.org>
Date:   Fri, 13 Oct 2023 13:58:57 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Neeraj Upadhyay <neeraj.upadhyay@....com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Uladzislau Rezki <urezki@...il.com>, rcu <rcu@...r.kernel.org>
Subject: [PATCH 13/18] rcu: Assume rcu_report_dead() is always called locally

rcu_report_dead() has to be called locally by the CPU that is going to
exit the RCU state machine. Passing a cpu argument here is error-prone
and leaves the possibility for a racy remote call.

Use local access instead.

Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 arch/arm64/kernel/smp.c  | 2 +-
 include/linux/rcupdate.h | 2 +-
 kernel/cpu.c             | 2 +-
 kernel/rcu/tree.c        | 4 ++--
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 960b98b43506..8fa646c90c67 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -401,7 +401,7 @@ void __noreturn cpu_die_early(void)
 
 	/* Mark this CPU absent */
 	set_cpu_present(cpu, 0);
-	rcu_report_dead(cpu);
+	rcu_report_dead();
 
 	if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
 		update_cpu_boot_status(CPU_KILL_ME);
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 5e5f920ade90..aa351ddcbe8d 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -122,7 +122,7 @@ static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
 void rcu_init(void);
 extern int rcu_scheduler_active;
 void rcu_sched_clock_irq(int user);
-void rcu_report_dead(unsigned int cpu);
+void rcu_report_dead(void);
 void rcutree_migrate_callbacks(int cpu);
 
 #ifdef CONFIG_TASKS_RCU_GENERIC
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6de7c6bb74ee..076e75fed8bb 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1388,7 +1388,7 @@ void cpuhp_report_idle_dead(void)
 	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 
 	BUG_ON(st->state != CPUHP_AP_OFFLINE);
-	rcu_report_dead(smp_processor_id());
+	rcu_report_dead();
 	st->state = CPUHP_AP_IDLE_DEAD;
 	/*
 	 * We cannot call complete after rcu_report_dead() so we delegate it
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8c2954502e55..2e1e7eadf2cc 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4560,11 +4560,11 @@ void rcu_cpu_starting(unsigned int cpu)
  * from the outgoing CPU rather than from the cpuhp_step mechanism.
  * This is because this function must be invoked at a precise location.
  */
-void rcu_report_dead(unsigned int cpu)
+void rcu_report_dead(void)
 {
 	unsigned long flags;
 	unsigned long mask;
-	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
 
 	/*
-- 
2.34.1