Re: [PATCH] kernel/cpu.c: Move the CPU_DYING notifiers

From: Avi Kivity
Date: Sat Sep 13 2008 - 02:36:18 EST

Manfred Spraul wrote:
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()
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.

kvm should work with this patch.

I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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