Commit bc8bcc79 authored Oct 22, 2008 by Lai Jiangshan Committed by Ingo Molnar Oct 22, 2008

x86/proc: fix /proc/cpuinfo cpu offline bug



Impact: fix missing CPUs in /proc/cpuinfo after CPU hotunplug/hotreplug

In my test, I found that if a cpu has been offline,
the next cpus may not be shown in the /proc/cpuinfo.

if one read() cannot consume the whole /proc/cpuinfo,
c_start() will be called again in the next read() calls.
And *pos has been increased by 1 by the caller(seq_read()).
if this time the cpu#*pos is offline, c_start() will return
NULL, and the next cpus can not be shown.

this fix use next_cpu_nr(*pos - 1, cpu_online_map) to
search the next unshown cpu.

the most easy way to reproduce this bug:
1) offline cpu#1             (cpu#0 is online)
2) dd ibs=2 if=/proc/cpuinfo
   the result is that only cpu#0 is shown.
   cpu#2 and cpu#3 .... cannot be shown in /proc/cpuinfo
   it's bug.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 35af2821

arch/x86/kernel/cpu/proc.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -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);
		}