Re: [Xen-devel] [RFC] KEXEC: allocate crash note buffers at boot time

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 29/11/11 11:19, Keir Fraser wrote:
> On 29/11/2011 18:56, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx> wrote:
>
>> Hello,
>>  
>> As I have little to no knowledge of this stage of the boot process, is
>> this a sensible way to be setting up the per_cpu areas?  I have a
>> sneaking suspicion that it will fall over if a CPU is onlined after
>> boot, and may also fall over if a CPU is offlined and reonlined later.
>> There appears to be no infrastructure currently in place for this type
>> of initialization, which is quite possibly why the code exists in its
>> current form.
> No it's bad. For starters you should use for_each_online_cpu, not do an
> open-coded for-loop. Secondly you should register a cpu hotplug notifier
> (register_cpu_notifier()) to pick up and handle future
> CPU_UP_PREPARE/CPU_UP_CANCELED/CPU_DEAD events. This can be hung off an
> __initcall. See common/stop_machine.c for example, or common/timer.c, which
> doesn't even require a for_each_online_cpu loop because its init code gets
> run before we bring up secondary CPUs.
>
>  -- Keir 
>

Thanks - this is exactly what I was looking for.

Sadly, after thinking about cpu hotplug safety, it is not safe to store
the crash note pointer in the per cpu data.  Once you have reported an
area to dom0 via KEXEC_CMD_get_reserve, the areas reported cant possibly
move.

Therefore, I need to redesign a little bit.

Thanks,

~Andrew

>> Thanks,
>

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com


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