linux-kernel - RE: [PATCH] Fix the race between smp_call

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Date:	Fri, 23 Mar 2012 11:32:43 +0000
From:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: RE: [PATCH] Fix the race between smp_call_function and CPU booting

In fact, I started two scripts running:
1/ One script:
echo 0 > /sys/devices/system/cpuX/online
echo 1 > /sys/devices/system/cpuX/online
Rerunning the above commands in loop

2/Another script:
echo 1 > /debug/smp_call_test
usleep 50000
Rerunning the above command in loop

This race issue can be easy to be reproduced in several minutes;
For simplify your test as mine(just two CPUs), you can set other non-booting CPUs as offline
at first and just leave one non-booting CPU.

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Friday, March 23, 2012 6:26 PM
> To: Liu, Chuansheng
> Cc: linux-kernel@...r.kernel.org; Yanmin Zhang; tglx@...utronix.de; Srivatsa S.
> Bhat
> Subject: RE: [PATCH] Fix the race between smp_call_function and CPU booting
> 
> On Thu, 2012-03-22 at 00:59 +0000, Liu, Chuansheng wrote:
> > Below is the complete test patch. Just run the simpl_loop_onoffline.sh
> > and simpl_loop_smpcalling.sh concurrently to reproduce the race.
> >
> What I did was:
> 
> for i in {2..23} ; do echo 0 > /sys/devices/system/cpu/cpu${i}/online ; done while
> usleep 50000 ; do echo 1 > /debug/smp_call_test ; done & while :; do echo $i >
> /sys/devices/system/cpu/cpu1/online ; let i^=1 ; done
> 
> and this has been running for well over 30 minutes.. is there anything else one
> needs to do?
> 

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