linux-kernel - Re: [PATCH] kernel/cpu.c: Move the CPU

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Message-ID: <48CB5F56.5050001@qumranet.com>
Date:	Sat, 13 Sep 2008 09:36:06 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Manfred Spraul <manfred@...orfullife.com>
CC:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org
Subject: Re: [PATCH] kernel/cpu.c: Move the CPU_DYING notifiers

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()
> 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.
>
>   

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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