linux-kernel - Re: [PATCH 1/1] sched: fix cpu

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Date:	Fri, 11 Sep 2009 15:38:15 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	peterz@...radead.org, rjw@...k.pl, akpm@...ux-foundation.org,
	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 1/1] sched: fix cpu_down deadlock

Jiri Slaby wrote:
> On 09/11/2009 08:09 AM, Lai Jiangshan wrote:
>> Does this bug occur when a cpu is being offlined or
>> when the system is being suspended?
>> Or Both?
> 
> Hi, I tried echo 0/1 > /sys/devices/system/cpu/cpu1/online in a loop,
> but it didn't trigger the bug. It happened only on suspend/resume cycle
> (in the end I found even swsusp in qemu suffers from this).
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> 

OK, I knew where this bug is.

I thought the corresponding bit in cpu_active_mask is cleared before
_cpu_down(), but I missed the system-suspend path:disable_nonboot_cpus().

There is a bug in disable_nonboot_cpus() even if my patch is removed.

cpu_active_map is wrong during suspending.(scheduler system who uses
cpu_active_map are still working while suspending)

You need:

int disable_nonboot_cpus(void)
{
	....
	....

	/*
	 * You need adding 'set_cpu_active(cpu, false);' here
	 * to fix this bug and make my patch works well.
	 */
	error = _cpu_down(cpu, 1);

	....
	....
}

Lai.

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