linux-kernel - Re: [PATCH v3 5/9] powerpc: Use preempt_model

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Message-ID: <deb0d4fa-d2ec-4acc-b217-b5ebb683bf05@csgroup.eu>
Date: Sun, 9 Feb 2025 19:42:07 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
 Ben Segall <bsegall@...gle.com>, Catalin Marinas <catalin.marinas@....com>,
 Dietmar Eggemann <dietmar.eggemann@....com>, Ingo Molnar <mingo@...hat.com>,
 Juri Lelli <juri.lelli@...hat.com>, Mel Gorman <mgorman@...e.de>,
 Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>,
 Thomas Gleixner <tglx@...utronix.de>,
 Valentin Schneider <vschneid@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>, Will Deacon <will@...nel.org>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Naveen N Rao <naveen@...nel.org>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 5/9] powerpc: Use preempt_model_str().

Le 09/02/2025 à 15:38, Shrikanth Hegde a écrit :
> 
> 
> On 2/8/25 23:25, Christophe Leroy wrote:
>>
>>
>> Le 08/02/2025 à 14:42, Shrikanth Hegde a écrit :
>>>
>>>
>>> On 2/8/25 18:25, Christophe Leroy wrote:
>>>>
>>>>
>>>> Le 08/02/2025 à 08:35, Shrikanth Hegde a écrit :
>>>>>
>>>>>
>>>>> On 2/4/25 13:52, Sebastian Andrzej Siewior wrote:
>>>>>> Use preempt_model_str() instead of manually conducting the preemption
>>>>>> model. Use pr_emerg() instead of printk() to pass a loglevel.
>>>>>
>>>>> even on powerpc, i see __die ends up calling show_regs_print_info().
>>>>> Why print it twice?
>>>>
>>>> I don't understand what you mean, what is printed twice ?
>>>>
>>>> I can't see show_regs_print_info() printing the preemption model, am 
>>>> I missing something ?
>>>>
>>>
>>> Patch 2/9 add preemption string in dump_stack_print_info.
>>>
>>> __die -> show_regs() _> show_regs_print_info() -> 
>>> dump_stack_print_info() -> init_utsname()->version, 
>>> preempt_model_str(), BUILD_ID_VAL);
>>>
>>> Wont we end up in this path?
>>
>> Indeed I missed that. You are right, we now get the information twice:
> 
> I think we can remove it from arch specific code and rely on lib/ 
> dump_stack?

Yes I guess so.

> 
> And similar concern of printk vs pr_warn/pr_emerg would apply to that as 
> well i guess.

Well, powerpc's show_regs() calls it with 
show_regs_print_info(KERN_DEFAULT);

And dump_stack_print_info() uses printk with log_lvl so there should be 
no concern here.

> 
>>
>> [  440.068216] BUG: Unable to handle kernel data access on write at 
>> 0xc09036fc