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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
        xen-devel@lists.xenproject.org,
        Daniel Lezcano <daniel.lezcano@linaro.org>
Subject: Re: [PATCH] cpuidle: Check for dev before deregistering it.
Date: Tue, 03 Dec 2013 22:33:08 +0100
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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@rjwysocki.net>
> CC: Daniel Lezcano <daniel.lezcano@linaro.org>
> CC: linux-pm@vger.kernel.org
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.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();
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.