linux-kernel - RE: Re: FW: [4.12 regression] "cpufreq: intel_pstate: Active mode P-state limits rework"

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Date:   Thu, 01 Jun 2017 01:08:16 +0000
From:   Jongman Heo <jongman.heo@...sung.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
CC:     Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: RE: Re: FW: [4.12 regression]
 "cpufreq: intel_pstate: Active mode P-state limits rework"

> 
>--------- Original Message ---------
>Sender : Rafael J. Wysocki <rjw@...ysocki.net>
>Date   : 2017-06-01 08:58 (GMT+9)
>Title  : Re: FW: [4.12 regression] "cpufreq: intel_pstate: Active mode P-state limits rework"
> 
>On Monday, May 29, 2017 02:18:52 AM Jongman Heo wrote:
>> 
>> Hi,
>> 
>> FYI, 4.12-rc3 still has this issue.
>> 
>>  
>> --------- Original Message ---------
>> Sender : 허종만 <jongman.heo@...sung.com>
>> Date   : 2017-05-16 13:25 (GMT+9)
>> Title  : [4.12 regression] "cpufreq: intel_pstate: Active mode P-state limits rework"
>>  
>>  
>> Hi,
>>  
>> With 4.12-rc1 (Linus git), booting fails due to kernel panic, at intel_pstate_register_driver+0x56/0x110.
>> I can't copy the whole trace from the graphic console, it looks like below.
>>  
>> Call Trace:
>>   intel_pstate_init
>>   intel_pstate_setup
>>   do_one_initcall
>>   set_debug_rodata
>>   kernel_init_freeable
>>   rest_init
>>   kernel_init
>>   ret_from_fork
>>     Code: ...
>>   RIP: intel_pstate_register_driver+0x56/0x110 RSP: ffffa3a98000bd80
>>   ...
> 
>I guess this is a division by 0 due to the unmet assumption that the denominator
>in min_perf_pct_min() will always be nonzero.
> 
>If this guess is correct, the patch below should help, so can you please test it?
> 
>Thanks,
>Rafael
> 
> 
>---
> drivers/cpufreq/intel_pstate.c |    5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
> 
>Index: linux-pm/drivers/cpufreq/intel_pstate.c
>===================================================================
>--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
>+++ linux-pm/drivers/cpufreq/intel_pstate.c
>@@ -571,9 +571,10 @@ static inline void update_turbo_state(vo
> static int min_perf_pct_min(void)
> {
>         struct cpudata *cpu = all_cpu_data[0];
>+        int turbo_pstate = cpu->pstate.turbo_pstate;
> 
>-        return DIV_ROUND_UP(cpu->pstate.min_pstate * 100,
>-                            cpu->pstate.turbo_pstate);
>+        return turbo_pstate ?
>+                DIV_ROUND_UP(cpu->pstate.min_pstate * 100, turbo_pstate) : 0;
> }
> 
> static s16 intel_pstate_get_epb(struct cpudata *cpu_data)
> 
> 
> 

Hi,

Your patch fixes the issue.
Thanks~.

Jongman.