Re: [PATCH] x86/proc: fix /proc/cpuinfo cpu offline bug

From: Alexey Dobriyan
Date: Fri Oct 17 2008 - 07:38:40 EST


On Fri, Oct 17, 2008 at 04:55:25PM +0800, Lai Jiangshan wrote:
> In my test, I found that if a cpu has been offline,
> the next cpus may not be shown in the /proc/cpuinfo.
>
> trivially reproduce this bug:
>
> 1) add these lines in the end of show_cpuinfo()
> if (m->size - m->count - 20 > 0)
> seq_printf(m, "%*s", (int)(m->size - m->count - 20), "show bug\n");

What is it?

Can you just show wrong /proc/cpuinfo ?

Can someone with at least 4-way box please do so?

> 3) offline cpu#1
> 4) cat /proc/cpuinfo
> cpu#2 and cpu#3 .... cannot be shown in /proc/cpuinfo

> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -160,14 +160,16 @@ static void *c_start(struct seq_file *m, loff_t *pos)
> {
> if (*pos == 0) /* just in case, cpu 0 is not the first */
> *pos = first_cpu(cpu_online_map);
> - if ((*pos) < nr_cpu_ids && cpu_online(*pos))
> + else
> + *pos = next_cpu_nr(*pos - 1, cpu_online_map);
> + if ((*pos) < nr_cpu_ids)
> return &cpu_data(*pos);
> return NULL;
> }
>
> static void *c_next(struct seq_file *m, void *v, loff_t *pos)
> {
> - *pos = next_cpu(*pos, cpu_online_map);
> + (*pos)++;
> return c_start(m, pos);
> }
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