Commit 3ba35573 authored Aug 31, 2008 by Manfred Spraul Committed by Ingo Molnar Sep 06, 2008

kernel/cpu.c: Move the CPU_DYING notifiers



When a cpu is taken offline, the CPU_DYING notifiers are called on the
dying cpu. According to <linux/notifiers.h>, the cpu should be "not
running any task, not handling interrupts, soon dead".

For the current implementation, this is not true:
- __cpu_disable can fail. If it fails, then the cpu will remain alive
  and happy.
- At least on x86, __cpu_disable() briefly enables the local interrupts
  to handle any outstanding interrupts.

What about moving CPU_DYING down a few lines, behind the __cpu_disable()
line?
There are only two CPU_DYING handlers in the kernel right now: one in
kvm, one in the scheduler. Both should work with the patch applied
[and: I'm not sure if either one handles a failing __cpu_disable()]

The patch survives simple offlining a cpu. kvm untested due to lack
of a test setup.

Signed-off-By: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 38736f47

kernel/cpu.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -199,13 +199,14 @@ static int __ref take_cpu_down(void *_param)
		struct take_cpu_down_param *param = _param;
		int err;

		raw_notifier_call_chain(&cpu_chain, CPU_DYING \| param->mod,
		param->hcpu);
		/* Ensure this CPU doesn't handle any more interrupts. */
		err = __cpu_disable();
		if (err < 0)
		return err;

		raw_notifier_call_chain(&cpu_chain, CPU_DYING \| param->mod,
		param->hcpu);

		/* Force idle task to run as soon as we yield: it should
		immediately notice cpu is offline and die quickly. */
		sched_idle_next();

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