Commit d19b3ad0 authored by Daniel Henrique Barboza's avatar Daniel Henrique Barboza Committed by Michael Ellerman
Browse files

powerpc/pseries/hotplug-cpu: Show 'last online CPU' error in dlpar_cpu_offline() 



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.

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, eturning a more informative error
message:

  pseries-hotplug-cpu: Unable to remove last online CPU PowerPC,POWER9

Signed-off-by: default avatarDaniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210323205056.52768-2-danielhb413@gmail.com
parent dfc4ae33

arch/powerpc/platforms/pseries/hotplug-cpu.c

+14 −0
Original line number Diff line number Diff line
@@ -271,6 +271,19 @@ static int dlpar_offline_cpu(struct device_node *dn) 
			if (!cpu_online(cpu))

				break;



			/*

			 * device_offline() will return -EBUSY (via cpu_down()) if there

			 * is only one CPU left. Check it here to fail earlier and with a

			 * more informative error message, while also retaining the

			 * cpu_add_remove_lock to be sure that no CPUs are being

			 * online/offlined during this check.

			 */

			if (num_online_cpus() == 1) {

				pr_warn("Unable to remove last online CPU %pOFn\n", dn);

				rc = -EBUSY;

				goto out_unlock;

			}



			cpu_maps_update_done();

			rc = device_offline(get_cpu_device(cpu));

			if (rc)
@@ -283,6 +296,7 @@ static int dlpar_offline_cpu(struct device_node *dn) 
				thread);

		}

	}

out_unlock:

	cpu_maps_update_done();



out: