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

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Message-ID: <CA+ydwtqrZ0GVN24M8zEZhWuTqvRASpqSHTYWfoDrTHFAJZGp5Q@mail.gmail.com>
Date:   Wed, 10 May 2017 22:16:33 +0300
From:   Tommi Rantala <tt.rantala@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        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

2017-05-10 17:30 GMT+03:00 Thomas Gleixner <tglx@...utronix.de>:
> 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>

Many thanks, I can confirm that it works well!

-Tommi

> ---
>  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;