Fix PREEMPT_RCU without HOTPLUG_CPU

PREEMPT_RCU without HOTPLUG_CPU is broken. The rcu_online_cpu is called to initially populate rcu_cpu_online_map with all online CPUs when the hotplug event handler is installed, and also to populate the map with CPUs as they come online. The former case is meant to happen with and without HOTPLUG_CPU, but without HOTPLUG_CPU, the rcu_offline_cpu function is no-oped -- while it still gets called, it does not set the rcu CPU map. With a blank RCU CPU map, grace periods get to tick by completely oblivious to active RCU read side critical sections. This results in free-before-grace bugs. Fix is obvious once the problem is known. (Also, change __devinit to __cpuinit so the function gets thrown away on !HOTPLUG_CPU kernels).

Nick Piggin committed 18 years ago

Commit 70ff0551 parent eb6d42e1 file · +8 −12Browse files

Showing the changes to kernel (1 of 1 file). Show all

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kernel/rcupreempt.c+8−12

@@ -925,26 +925,22 @@ void rcu_offline_cpu(int cpu) · 924 unmodified lines
925	925	spin_unlock_irqrestore(&rdp->lock, flags);
926	926	}
927	927
928		−void __devinit rcu_online_cpu(int cpu)
929		−{
930		− unsigned long flags;
931		−
932		− spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
933		− cpu_set(cpu, rcu_cpu_online_map);
934		− spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
935		−}
936		−
937	928	#else /* #ifdef CONFIG_HOTPLUG_CPU */
938	929
939	930	void rcu_offline_cpu(int cpu)
940	931	{
941	932	}
942	933
943		−void __devinit rcu_online_cpu(int cpu)
	934	+#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
	935	+
	936	+void __cpuinit rcu_online_cpu(int cpu)
944	937	{
945		−}
	938	+ unsigned long flags;
946	939
947		−#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
	940	+ spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
	941	+ cpu_set(cpu, rcu_cpu_online_map);
	942	+ spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
	943	+}
948	944
949	945	static void rcu_process_callbacks(struct softirq_action *unused)
950	946	{