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

* Lai Jiangshan <laijs@cn.fujitsu.com> wrote:

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

fix is already upstream - see below.

Ingo

-------------------->
Gitweb: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=bc8bcc79ea4203c7d04309f1307ab88c86f0b0cf
Commit: bc8bcc79ea4203c7d04309f1307ab88c86f0b0cf
Parent: 35af28219e684a36cc8b1ff456c370ce22be157d
Author: Lai Jiangshan <laijs@cn.fujitsu.com>
AuthorDate: Wed Oct 22 12:42:30 2008 +0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed Oct 22 14:29:37 2008 +0200

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>
---
arch/x86/kernel/cpu/proc.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index a26c480..01b1244 100644
--- 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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