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@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Author: Frederic Weisbecker

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);

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

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

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. */
 
 	/*