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

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Message-ID: <b95272d4-e593-48e9-aa32-8758394f4b61@linux.ibm.com>
Date: Sun, 9 Feb 2025 20:08:22 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>,
        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().



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?

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

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