linux-kernel - Re: [PATCH V3] cpuidle: check dev before usage in cpuidle_use_deepest

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Message-ID: <20170504101608.GA5252@mai>
Date:   Thu, 4 May 2017 12:16:08 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "Li, Fei" <fei.li@...el.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Shi, FengX" <fengx.shi@...el.com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Koul, Vinod" <vinod.koul@...el.com>
Subject: Re: [PATCH V3] cpuidle: check dev before usage in
 cpuidle_use_deepest_state

On Thu, May 04, 2017 at 09:00:52AM +0000, Li, Fei wrote:
> In case of there is no cpuidle devices registered, dev will be null, and 
> panic will be triggered like below;
> In this patch, add checking of dev before usage, like that done in
> cpuidle_idle_call.
> 
> Panic without fix:
> [  184.961328] BUG: unable to handle kernel NULL pointer dereference at
>   (null)
> [  184.961328] IP: cpuidle_use_deepest_state+0x30/0x60
> ...
> [  184.961328]  play_idle+0x8d/0x210
> [  184.961328]  ? __schedule+0x359/0x8e0
> [  184.961328]  ? _raw_spin_unlock_irqrestore+0x28/0x50
> [  184.961328]  ? kthread_queue_delayed_work+0x41/0x80
> [  184.961328]  clamp_idle_injection_func+0x64/0x1e0
> 
> Fixes: bb8313b603eb8 ("cpuidle: Allow enforcing deepest idle state selection")
> Signed-off-by: Li, Fei <fei.li@...el.com>
> Tested-by: Shi, Feng <fengx.shi@...el.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Reviewed-by: Koul, Vinod <vinod.koul@...el.com>
> ---
>  drivers/cpuidle/cpuidle.c | 3 ++- 
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 548b90b..2706be7 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -111,7 +111,8 @@ void cpuidle_use_deepest_state(bool enable)
>  
>     preempt_disable();
>     dev = cpuidle_get_device();
> -   dev->use_deepest_state = enable;
> +   if (dev)
> +       dev->use_deepest_state = enable;


This change is acceptable as a hot fix but the question is 'why is this
function called if there is no cpuidle driver registered?'

>     preempt_enable();
>  }
>  
> -- 
> 1.9.1
> 
> Best Regards,
> Fei

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