Re: [PATCH] LoongArch: Do not create sysfs control file for io master CPUs

[Tiezhu Yang]

On 10/08/2022 05:27 PM, WANG Xuerui wrote:
> On 2022/10/8 16:59, Tiezhu Yang wrote:
> > Now io master CPUs are not hotpluggable on LoongArch, in the current
> > code,
> > only /sys/devices/system/cpu/cpu0/online is not created, let us set the
> > hotpluggable field of all the io master CPUs as 0, then prevent to create
> > sysfs control file for the other io master CPUs which confuses some user
> > space tools. This is similar with commit 9cce844abf07 ("MIPS: CPU#0 is
> > not
> > hotpluggable").
> >
> > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> > ---
> >   arch/loongarch/kernel/smp.c      |  8 --------
> >   arch/loongarch/kernel/topology.c | 12 +++++++++++-
> >   2 files changed, 11 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> > index b5fab30..ef89292 100644
> > --- a/arch/loongarch/kernel/smp.c
> > +++ b/arch/loongarch/kernel/smp.c
> > @@ -240,19 +240,11 @@ void loongson3_smp_finish(void)
> >     #ifdef CONFIG_HOTPLUG_CPU
> >   -static bool io_master(int cpu)
> > -{
> > -    return test_bit(cpu, &loongson_sysconf.cores_io_master);
> > -}
> > -
> >   int loongson3_cpu_disable(void)
> >   {
> >       unsigned long flags;
> >       unsigned int cpu = smp_processor_id();
> >   -    if (io_master(cpu))
> > -        return -EBUSY;
> > -
>
> Could this get invoked from somewhere other than the sysfs entries that
> "confuse user-space tools", e.g. from somewhere else in kernel land? If
> so (or if we can't rule out the possibility) keeping the guard here
> might prove more prudent.

If c->hotpluggable is 0, it will not generate a control file in sysfs
for this CPU, for example:

[root@linux loongson]# cat /sys/devices/system/cpu/cpu0/online
cat: /sys/devices/system/cpu/cpu0/online: No such file or directory
[root@linux loongson]# echo 0 > /sys/devices/system/cpu/cpu0/online
bash: /sys/devices/system/cpu/cpu0/online: Permission denied

So no need to check it here, just remove the code.

This was done in commit cbab54d9c2b2 ("MIPS: No need to check CPU 0 in
{loongson3,bmips,octeon}_cpu_disable()").

> >   #ifdef CONFIG_NUMA
> >       numa_remove_cpu(cpu);
> >   #endif
> > diff --git a/arch/loongarch/kernel/topology.c
> > b/arch/loongarch/kernel/topology.c
> > index ab1a75c..7e7a77f 100644
> > --- a/arch/loongarch/kernel/topology.c
> > +++ b/arch/loongarch/kernel/topology.c
> > @@ -5,6 +5,7 @@
> >   #include <linux/node.h>
> >   #include <linux/nodemask.h>
> >   #include <linux/percpu.h>
> > +#include <asm/bootinfo.h>
> >     static DEFINE_PER_CPU(struct cpu, cpu_devices);
> >   @@ -33,6 +34,11 @@ void arch_unregister_cpu(int cpu)
> >   EXPORT_SYMBOL(arch_unregister_cpu);
> >   #endif
> >   +static bool io_master(int cpu)
> > +{
> > +    return test_bit(cpu, &loongson_sysconf.cores_io_master);
> > +}
> > +
> >   static int __init topology_init(void)
> >   {
> >       int i, ret;
> > @@ -40,7 +46,11 @@ static int __init topology_init(void)
> >       for_each_present_cpu(i) {
> >           struct cpu *c = &per_cpu(cpu_devices, i);
> >   -        c->hotpluggable = !!i;
> > +        if (io_master(i))
> > +            c->hotpluggable = 0;
> > +        else
> > +            c->hotpluggable = 1;
> > +
>
> This is just "c->hotpluggable = !io_master(i);".

Yes, I am OK either way, if it is necessary to send v2,
please let me know.

> >           ret = register_cpu(c, i);
> >           if (ret < 0)
> >               pr_warn("topology_init: register_cpu %d failed (%d)\n",
> > i, ret);
> Other changes should be okay as they are in line with the previous MIPS
> change you referenced, but let's see what Huacai thinks.

Thanks,
Tiezhu