linux-kernel - Re: [PATCH] hwmon: (coretemp) Handle frozen hotplug state correctly

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Message-ID: <20170510200917.GA5628@roeck-us.net>
Date:   Wed, 10 May 2017 13:09:17 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Tommi Rantala <tt.rantala@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Subject: Re: [PATCH] hwmon: (coretemp) Handle frozen hotplug state correctly

On Wed, May 10, 2017 at 04:30:12PM +0200, Thomas Gleixner wrote:
> The recent conversion to the hotplug state machine missed that the original
> hotplug notifiers did not execute in the frozen state, which is used on
> suspend on resume.
> 
> This does not matter on single socket machines, but on multi socket systems
> this breaks when the device for a non-boot socket is removed when the last
> CPU of that socket is brought offline. The device removal locks up the
> machine hard w/o any debug output.
> 
> Prevent executing the hotplug callbacks when cpuhp_tasks_frozen is true.
> 
> Thanks to Tommi for providing debug information patiently while I failed to
> spot the obvious.
> 
> Fixes: e00ca5df37ad ("hwmon: (coretemp) Convert to hotplug state machine")
> Reported-by: Tommi Rantala <tt.rantala@...il.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Applied, and thanks a lot for fixing the problem!

Guenter

> ---
>  drivers/hwmon/coretemp.c |   14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> --- a/drivers/hwmon/coretemp.c
> +++ b/drivers/hwmon/coretemp.c
> @@ -605,6 +605,13 @@ static int coretemp_cpu_online(unsigned
>  	struct platform_data *pdata;
>  
>  	/*
> +	 * Don't execute this on resume as the offline callback did
> +	 * not get executed on suspend.
> +	 */
> +	if (cpuhp_tasks_frozen)
> +		return 0;
> +
> +	/*
>  	 * CPUID.06H.EAX[0] indicates whether the CPU has thermal
>  	 * sensors. We check this bit only, all the early CPUs
>  	 * without thermal sensors will be filtered out.
> @@ -654,6 +661,13 @@ static int coretemp_cpu_offline(unsigned
>  	struct temp_data *tdata;
>  	int indx, target;
>  
> +	/*
> +	 * Don't execute this on suspend as the device remove locks
> +	 * up the machine.
> +	 */
> +	if (cpuhp_tasks_frozen)
> +		return 0;
> +
>  	/* If the physical CPU device does not exist, just return */
>  	if (!pdev)
>  		return 0;
> --
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