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

[Daniel Henrique Barboza]

Ping

On 3/5/21 2:38 PM, Daniel Henrique Barboza wrote:
> Of all the reasons that dlpar_cpu_remove() can fail, the 'last online
> CPU' is one that can be caused directly by the user offlining CPUs
> in a partition/virtual machine that has hotplugged CPUs. Trying to
> reclaim a hotplugged CPU can fail if the CPU is now the last online in
> the system. This is easily reproduced using QEMU [1].
> 
> 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.
> 
> [1] https://bugzilla.redhat.com/1911414
> 
> Signed-off-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
> ---
>   arch/powerpc/platforms/pseries/hotplug-cpu.c | 12 +++++++++++-
>   1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> index 12cbffd3c2e3..134f393f09e1 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> @@ -514,7 +514,17 @@ static ssize_t dlpar_cpu_remove(struct device_node *dn, u32 drc_index)
>   
>   	rc = dlpar_offline_cpu(dn);
>   	if (rc) {
> -		pr_warn("Failed to offline CPU %pOFn, rc: %d\n", dn, rc);
> +		/* dlpar_offline_cpu will return -EBUSY from cpu_down() (via
> +		 * device_offline()) in 2 cases: cpu_hotplug_disable is true or
> +		 * there is only one CPU left. Warn the user about the second
> +		 * since this can happen with user offlining CPUs and then
> +		 * attempting hotunplugs.
> +		 */
> +		if (rc == -EBUSY && num_online_cpus() == 1)
> +			pr_warn("Unable to remove last online CPU %pOFn\n", dn);
> +		else
> +			pr_warn("Failed to offline CPU %pOFn, rc: %d\n", dn, rc);
> +
>   		return -EINVAL;
>   	}
>   
>