[Xen-devel] Re: CPU offlining patch xen-unstable:21049

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 15/04/2010 09:50, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:

> I think the try_lock is not for the cpu_down(). The point is, if another CPU
> is trying the get the lock.
> 
> Considering following scnerio:
> 1) cpu_down() in CPU A, and get the xenpf_lock, then call to
> stop_machine_run(), trying to bring all CPU to stop_machine_run context.
> 2) At the same time, another vcpu in CPU B do a xenpf hypercall, and try to
> get the xenpf_lock. If ther is no retyr for this lock, it can't get
> xenpf_lock, it will never go to the softirq
> So the system will hang.
> 
> Hope this make thing clear.

But CPU A doesn't hold the xenpf_lock when it calls stop_machine_run(). It
dropped it before cpu_down() got invoked, because that gets executed via
continue_hypercall_on_cpu().

 -- Keir



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