Re: [PATCH v3 1/1] hotplug-cpu.c: show 'last online CPU' error in dlpar_cpu_offline()

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 <redacted>

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 <redacted>

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