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

[Jongman Heo <jongman.heo@samsung.com>]

> 
>--------- Original Message ---------
>Sender : Rafael J. Wysocki <rjw@rjwysocki.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@samsung.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.