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Subject: Re: [PATCH v3 1/1] hotplug-cpu.c: show 'last online CPU' error in
 dlpar_cpu_offline()
To: Daniel Henrique Barboza <danielhb413@gmail.com>,
 linuxppc-dev@lists.ozlabs.org
References: <20210326141954.236323-1-danielhb413@gmail.com>
 <20210326141954.236323-2-danielhb413@gmail.com>
From: Andrew Donnellan <ajd@linux.ibm.com>
Message-ID: <3155bcf5-26a5-b036-590f-02052eaacbf4@linux.ibm.com>
Date: Sat, 27 Mar 2021 02:30:18 +1100
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On 27/3/21 1:19 am, Daniel Henrique Barboza wrote:
> One of the reasons that dlpar_cpu_offline can fail is when attempting to
> offline the last online CPU of the kernel. This can be observed in a
> pseries QEMU guest that has hotplugged CPUs. If the user offlines all
> other CPUs of the guest, and a hotplugged CPU is now the last online
> CPU, trying to reclaim it will fail. See [1] for an example.
> 
> The current error message in this situation returns rc with -EBUSY and a
> generic explanation, e.g.:
> 
> pseries-hotplug-cpu: Failed to offline CPU PowerPC,POWER9, rc: -16
> 
> EBUSY can be caused by other conditions, such as cpu_hotplug_disable
> being true. Throwing a more specific error message for this case,
> instead of just "Failed to offline CPU", makes it clearer that the error
> is in fact a known error situation instead of other generic/unknown
> cause.
> 
> This patch adds a 'last online' check in dlpar_cpu_offline() to catch
> the 'last online CPU' offline error, returning a more informative error
> message:
> 
> pseries-hotplug-cpu: Unable to remove last online CPU PowerPC,POWER9
> 
> [1] https://bugzilla.redhat.com/1911414
> 
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

Thanks for addressing the issues in Daniel's review.

I haven't tested it, but this patch looks sensible enough to me.

Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>

-- 
Andrew Donnellan              OzLabs, ADL Canberra
ajd@linux.ibm.com             IBM Australia Limited