linux-kernel - Re: [lm-sensors] [PATCH] x86/hwmon: fix module init for hotplug-but-no-device-found case

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Date:	Tue, 14 Sep 2010 07:47:48 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Chen Gong" <gong.chen@...ux.intel.com>
Cc:	<fenghua.yu@...el.com>, <khali@...ux-fr.org>,
	<lm-sensors@...sensors.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [lm-sensors] [PATCH] x86/hwmon: fix module init
	 for		hotplug-but-no-device-found case

>>> On 14.09.10 at 08:30, Chen Gong <gong.chen@...ux.intel.com> wrote:
> 于 9/13/2010 6:05 PM, Jan Beulich 写道:
>> In commit 0dca94baeab4a1a514841b0a4c8e3a51dfb4d5ae the call to
>> platform_driver_unregister() was made conditional upon !HOTPLUG_CPU,
>> but the return value from coretemp_init() was left to indicate an
>> error. This isn't correct, as the negative return value indicates to
>> the module loader that initialization failed, which isn't intended
> 
> only !HOTPLUG_CPU can remove the driver. That is what we need to do 
> because under the hotplug condition, we need to consider those "offline"
> cpus. I don't understand what you are afraid. Can you give me a scinario ?

If the driver's init routine returns -ENODEV (like is the case without this
change when HOTPLUG_CPU is enabled and there is no device found),
the platform driver will remain registered, yet the driver memory will
get freed (leaving dangling pointers into the driver's former image). Or
in other words - when leaving the driver registered, the return value
of the init function must be zero.

Jan

>> here and results in dangling pointers.
>>
>> Signed-off-by: Jan Beulich<jbeulich@...ell.com>
>> Cc: Chen Gong<gong.chen@...ux.intel.com>
>>
>> ---
>>   drivers/hwmon/coretemp.c |    5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> --- linux-2.6.36-rc4/drivers/hwmon/coretemp.c	2010-09-13 08:45:02.000000000 
> +0200
>> +++ 
> 2.6.36-rc4-x86-coretemp-hotplug-init-return/drivers/hwmon/coretemp.c	2010-
> 09-03 17:54:14.000000000 +0200
>> @@ -541,16 +541,19 @@ static int __init coretemp_init(void)
>>   				" has no thermal sensor.\n", c->x86_model);
>>   		}
>>   	}
>> +
>> +#ifndef CONFIG_HOTPLUG_CPU
>>   	if (list_empty(&pdev_list)) {
>>   		err = -ENODEV;
>>   		goto exit_driver_unreg;
>>   	}
>> +#endif
>>
>>   	register_hotcpu_notifier(&coretemp_cpu_notifier);
>>   	return 0;
>>
>> -exit_driver_unreg:
>>   #ifndef CONFIG_HOTPLUG_CPU
>> +exit_driver_unreg:
>>   	platform_driver_unregister(&coretemp_driver);
>>   #endif
>>   exit:
>>
>>
>>
>>


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