On Sat, Jul 25, 2020 at 04:29:28PM +0800, Huacai Chen wrote:
> Hi, Greg,
>
> On Sat, Jul 25, 2020 at 3:45 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Sat, Jul 25, 2020 at 02:57:31PM +0800, Huacai Chen wrote:
> > > Hi Greg,
> > >
> > > On Sat, Jul 25, 2020 at 2:49 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > > >
> > > > On Sat, Jul 25, 2020 at 02:37:52PM +0800, Huacai Chen wrote:
> > > > > Hi, Thomas,
> > > > >
> > > > > What do you think about this patch? Other archs also do the same thing
> > > > > except those support hotplug CPU#0.
> > > > >
> > > > > grep hotpluggable arch -rwI
> > > > > arch/riscv/kernel/setup.c: cpu->hotpluggable = cpu_has_hotplug(i);
> > > > > arch/powerpc/kernel/sysfs.c: BUG_ON(!c->hotpluggable);
> > > > > arch/powerpc/kernel/sysfs.c: c->hotpluggable = 1;
> > > > > arch/powerpc/kernel/sysfs.c: if (cpu_online(cpu) || c->hotpluggable) {
> > > > > arch/arm/kernel/setup.c: cpuinfo->cpu.hotpluggable =
> > > > > platform_can_hotplug_cpu(cpu);
> > > > > arch/sh/kernel/topology.c: c->hotpluggable = 1;
> > > > > arch/ia64/kernel/topology.c: * CPEI target, then it is hotpluggable
> > > > > arch/ia64/kernel/topology.c: sysfs_cpus[num].cpu.hotpluggable = 1;
> > > > > arch/xtensa/kernel/setup.c: cpu->hotpluggable = !!i;
> > > > > arch/s390/kernel/smp.c: c->hotpluggable = 1;
> > > > > arch/mips/kernel/topology.c: c->hotpluggable = 1;
> > > > > arch/arm64/kernel/cpuinfo.c: * In case the boot CPU is hotpluggable,
> > > > > we record its initial state and
> > > > > arch/arm64/kernel/setup.c: cpu->hotpluggable = cpu_can_disable(i);
> > > > > arch/x86/kernel/topology.c: per_cpu(cpu_devices,
> > > > > num).cpu.hotpluggable = 1;
> > > > >
> > > > > On Thu, Jul 16, 2020 at 6:38 PM Huacai Chen <chenhc@xxxxxxxxxx> wrote:
> > > > > >
> > > > > > Now CPU#0 is not hotpluggable on MIPS, so prevent to create /sys/devices
> > > > > > /system/cpu/cpu0/online which confuses some user-space tools.
> > > >
> > > > What userspace tools are confused by this? They should be able to
> > > > handle a cpu not being able to be removed, right?
> > > It causes ltp's "hotplug" test fails, and ltp considers CPUs with a
> > > "online" node be hotpluggable.
> >
> > Is that always true?
> Yes, someone who meet the same problem report a bug to LTP, and LTP
> maintainer said that this should be fixed in kernel.
So the action _always_ has to succeed and can never return an error?
That feels wrong even for normal systems.
thanks,
greg k-h
