Messages in this thread Patch in this message | | | Date | Mon, 27 Oct 2008 14:11:49 +0800 | From | Lai Jiangshan <> | Subject | [PATCH resend] x86/proc: fix /proc/cpuinfo cpu offline bug |
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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 file, 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 uses next_cpu_nr(*pos - 1, cpu_online_map) to search the next unshown cpu.
the way to reproduce this bug: (cpu#0 cpu#1 cpu#2 must be online before test)
step 1) offline cpu#1 step 2) dd ibs=2 if=/proc/cpuinfo
now, only cpu#0 's cpuinfo is shown. cpu#2 and cpu#3 .... cannot be shown in /proc/cpuinfo it's a bug.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> --- 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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