Commit 70ff0555 authored Jul 10, 2008 by Nick Piggin Committed by Linus Torvalds Jul 10, 2008

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).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Reported-and-tested-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ Nick is my personal hero of the day - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent eb6d42ea

kernel/rcupreempt.c

+8 −12

Original line number	Diff line number	Diff line
		@@ -925,26 +925,22 @@ void rcu_offline_cpu(int cpu)
		spin_unlock_irqrestore(&rdp->lock, flags);
		}

		void __devinit rcu_online_cpu(int cpu)
		{
		unsigned long flags;

		spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
		cpu_set(cpu, rcu_cpu_online_map);
		spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
		}

		#else /* #ifdef CONFIG_HOTPLUG_CPU */

		void rcu_offline_cpu(int cpu)
		{
		}

		void __devinit rcu_online_cpu(int cpu)
		#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */

		void __cpuinit rcu_online_cpu(int cpu)
		{
		}
		unsigned long flags;

		#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
		spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
		cpu_set(cpu, rcu_cpu_online_map);
		spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
		}

		static void rcu_process_callbacks(struct softirq_action *unused)
		{

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