linux-kernel - Re: [PATCH] arch: s390: kernel: reset 'c->hotpluggable' when failure occurs

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Date:	Tue, 25 Jun 2013 17:31:27 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
CC:	Martin Schwidefsky <schwidefsky@...ibm.com>, linux390@...ibm.com,
	cornelia.huck@...ibm.com, mtosatti@...hat.com,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-s390@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] arch: s390: kernel: reset 'c->hotpluggable' when failure
 occurs

On 06/25/2013 05:09 PM, Heiko Carstens wrote:
> On Tue, Jun 25, 2013 at 03:24:09PM +0800, Chen Gang wrote:
>> On 06/25/2013 02:48 PM, Heiko Carstens wrote:
>>> On Tue, Jun 25, 2013 at 09:46:45AM +0800, Chen Gang wrote:
>>>>> When smp_add_present_cpu() fails, it has reset all things excluding
>>>>> 'c->hotpluggable', so need reset it as original state completely.
>>>>>
>>>>> +	c->hotpluggable = 0;
>>>>>  	return rc;
>>> No, that doesn't make sense. All cpus on s390 are always hotplugable.
>>> It really doesn't matter if the value of this field is 0 or 1 after
>>> an error.
>>>
>>
>> If so, is it better to set 'c->hotpluggable' for all cpus on s390 during
>> initializing ?
> 
> No, just leave the code as it is.
> 

Currently we have 3 possible states for 'struct cpu':
  initialized, and set hotplugable.
  unitialized, and set hotplugable.
  unitialized, and unset hotplugable.

Either 2nd or 3rd is inconsistent.

The cpu_is_hotplugable() will be used in kernel/rcutorture.c. I do not
know whether it will cause issue or not, but it seems dangerous when
__smp_rescan_cpus() has already called, and has some unsucessfull call
of smp_add_present_cpu().

Please help check.

Thanks.
-- 
Chen Gang

Asianux Corporation
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