[Xen-devel] Re: [PATCH]CPUFREQ: Fix two racing issues during cpu

To:	"Wei, Gang" <gang.wei@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	[Xen-devel] Re: [PATCH]CPUFREQ: Fix two racing issues during cpu hotplug
From:	Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date:	Mon, 12 Apr 2010 07:59:36 +0100
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On 12/04/2010 07:54, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:

>> Can't you just kill_timer()? Adding extra code into a stop_machine
>> context is dangerous: e.g.,
>> xmalloc()->alloc_xenheap_pages()->memguard_unguard_range()->map_pages_to_xen
>> ()->flush_area_all() results in deadlock as other cpus are spinning
>> with irqs disabled.
> 
> You are right. kill_timer stop timer and wait until timer handler end if this
> timer is current running. I can switch to it. BTW, I may need to re-init the
> killed timer before set_timer on it, right?

Yes, init_timer() must be called to be able to reuse a kill_timer()ed timer.

 -- Keir



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[Xen-devel] Re: [PATCH]CPUFREQ: Fix two racing issues during cpu hotplug