linux-kernel - Re: [PATCH] cpuidle: Check for dev before deregistering it.

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Date:	Wed, 04 Dec 2013 10:10:28 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] cpuidle: Check for dev before deregistering it.

On 12/03/2013 10:33 PM, Rafael J. Wysocki wrote:
> On Tuesday, December 03, 2013 10:59:58 AM Konrad Rzeszutek Wilk wrote:
>> If not, we could end up in the unfortunate situation where
>> we dereference a NULL pointer b/c we have cpuidle disabled.
>>
>> This is the case when booting under Xen (which uses the
>> ACPI P/C states but disables the CPU idle driver) - and can
>> be easily reproduced when booting with cpuidle.off=1.
>>
>> BUG: unable to handle kernel NULL pointer dereference at           (null)
>> IP: [<ffffffff8156db4a>] cpuidle_unregister_device+0x2a/0x90
>> .. snip..
>> Call Trace:
>>   [<ffffffff813b15b4>] acpi_processor_power_exit+0x3c/0x5c
>>   [<ffffffff813af0a9>] acpi_processor_stop+0x61/0xb6
>>   [<ffffffff814215bf>] __device_release_driver+0fffff81421653>] device_release_driver+0x23/0x30
>>   [<ffffffff81420ed8>] bus_remove_device+0x108/0x180
>>   [<ffffffff8141d9d9>] device_del+0x129/0x1c0
>>   [<ffffffff813cb4b0>] ? unregister_xenbus_watch+0x1f0/0x1f0
>>   [<ffffffff8141da8e>] device_unregister+0x1e/0x60
>>   [<ffffffff814243e9>] unregister_cpu+0x39/0x60
>>   [<ffffffff81019e03>] arch_unregister_cpu+0x23/0x30
>>   [<ffffffff813c3c51>] handle_vcpu_hotplug_event+0xc1/0xe0
>>   [<ffffffff813cb4f5>] xenwatch_thread+0x45/0x120
>>   [<ffffffff810af010>] ? abort_exclusive_wait+0xb0/0xb0
>>   [<ffffffff8108ec42>] kthread+0xd2/0xf0
>>   [<ffffffff8108eb70>] ? kthread_create_on_node+0x180/0x180
>>   [<ffffffff816ce17c>] ret_from_fork+0x7c/0xb0
>>   [<ffffffff8108eb70>] ? kthread_create_on_node+0x180/0x180
>>
>> This problem also appears in 3.12 and could be a candidate for backport.
>>
>> CC: "Rafael J. Wysocki" <rjw@...ysocki.net>
>> CC: Daniel Lezcano <daniel.lezcano@...aro.org>
>> CC: linux-pm@...r.kernel.org
>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>
> Applied, thanks!
>
>> ---
>>   drivers/cpuidle/cpuidle.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
>> index 2a991e4..a55e68f 100644
>> --- a/drivers/cpuidle/cpuidle.c
>> +++ b/drivers/cpuidle/cpuidle.c
>> @@ -400,7 +400,7 @@ EXPORT_SYMBOL_GPL(cpuidle_register_device);
>>    */
>>   void cpuidle_unregister_device(struct cpuidle_device *dev)
>>   {
>> -	if (dev->registered == 0)
>> +	if (!dev || dev->registered == 0)
>>   		return;
>>
>>   	cpuidle_pause_and_lock();

Oops, wait. Are we sure the problem is coming from cpuidle ?

The cpuidle_unregister_device is called with a NULL pointer, that 
shouldn't happen.

Konrad, you say that could be easily reproduced. How do you produce it ? 
Unplugging a cpu ?




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