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Subject: Re: Bug: d0e936adbd22 crashes at boot
To:     Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Len Brown <lenb@kernel.org>, inux-pm@vger.kernel.org
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 <3ac87893-55ba-f2d4-bb1e-382868f12d4c@kernel.dk>
 <7f115f0476618d34b24ddec772acbbd7c0c4a572.camel@linux.intel.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <767fe00f-bf31-1eb0-09cc-1be91c633bb4@kernel.dk>
Date:   Fri, 3 Sep 2021 09:00:33 -0600
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On 9/3/21 8:38 AM, Srinivas Pandruvada wrote:
> On Fri, 2021-09-03 at 08:15 -0600, Jens Axboe wrote:
>> On 9/3/21 8:13 AM, Srinivas Pandruvada wrote:
>>> Hi Axboe,
>>>
>>> Thanks for reporting.
>>> On Fri, 2021-09-03 at 07:36 -0600, Jens Axboe wrote:
>>>> Hi,
>>>>
>>>> Booting Linus's tree causes a crash on my laptop, an x1 gen9. This
>>>> was
>>>> a bit
>>>> difficult to pin down as it crashes before the display is up, but I
>>>> managed
>>>> to narrow it down to:
>>>>
>>>> commit d0e936adbd2250cb03f2e840c6651d18edc22ace
>>>> Author: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
>>>> Date:   Thu Aug 19 19:40:06 2021 -0700
>>>>
>>>>     cpufreq: intel_pstate: Process HWP Guaranteed change
>>>> notification
>>>>
>>>> which crashes with a NULL pointer deref in notify_hwp_interrupt() -
>>>>>
>>>> queue_delayed_work_on().
>>>>
>>>> Reverting this change makes the laptop boot fine again.
>>>>
>>> Does this change fixes your issue?
>>
>> I would assume so, as it's crashing on cpudata == NULL :-)
>>
>> But why is it NULL? Happy to test patches, but the below doesn't look
>> like
>> a real fix and more of a work-around.
> 
> This platform is sending an HWP interrupt on a CPU which we didn't yet
> bring it up for pstate control. So somehow firmware decided to send
> very early during boot, which previously we would have ignored it
> 
> Actually try this, with more prevention

I can give this a whirl.

> diff --git a/drivers/cpufreq/intel_pstate.c
> b/drivers/cpufreq/intel_pstate.c
> index b4ffe6c8a0d0..6ee88d7640ea 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1645,12 +1645,24 @@ void notify_hwp_interrupt(void)
>         if (!hwp_active || !boot_cpu_has(X86_FEATURE_HWP_NOTIFY))
>                 return;
>  
> -       rdmsrl(MSR_HWP_STATUS, value);
> +       rdmsrl_safe(MSR_HWP_STATUS, &value);
>         if (!(value & 0x01))
>                 return;
>  
> +       /*
> +        * After hwp_active is set and all_cpu_data is allocated, there
> +        * is small window.
> +        */
> +       if (!all_cpu_data) {
> +               wrmsrl_safe(MSR_HWP_STATUS, 0);
> +               return;
> +       }

What synchronizes the all_cpu_data setup and the interrupt? Can the
interrupt come in while it's still being setup?

-- 
Jens Axboe