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

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Date:   Sat, 8 Oct 2022 17:27:20 +0800
From:   WANG Xuerui <kernel@...0n.name>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Do not create sysfs control file for io master
 CPUs

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@...ngson.cn>
> ---
>   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.

>   #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);".

>   		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.

-- 
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/