linux-kernel - Re: [PATCH] panic: remove redundant panic-cpu backtrace

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Message-ID: <84pldghkho.fsf@jogness.linutronix.de>
Date: Thu, 31 Jul 2025 09:51:07 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, Andrew Morton
 <akpm@...ux-foundation.org>, Petr Mladek <pmladek@...e.com>, Feng Tang
 <feng.tang@...ux.alibaba.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] panic: remove redundant panic-cpu backtrace

On 2025-07-31, Sergey Senozhatsky <senozhatsky@...omium.org> wrote:
> On (25/07/31 09:15), John Ogness wrote:
>> On 2025-07-31, Sergey Senozhatsky <senozhatsky@...omium.org> wrote:
>> > SYS_INFO_ALL_CPU_BT sends NMI backtrace request to
>> > all CPUs, which dumps an extra backtrace on panic CPU.
>> 
>> Isn't this only true if CONFIG_DEBUG_BUGVERBOSE=y?
>
> Are you referring to vpanic()->dump_stack()?

Yes.

> Another way to get backtrace on panic CPU is via BUG(), which routes
> through die()->__die_body(), which prints registers, stack trace,
> and so on, before it calls into panic().  This might be x86 specific,
> though.

So in that case you see 2 stack traces if CONFIG_DEBUG_BUGVERBOSE=y?

>> Also, the information is not the same. trigger_all_cpu_backtrace() will
>> also dump the registers. For CONFIG_DEBUG_BUGVERBOSE=y on the panic CPU,
>> only the stack is dumped.
>
> Hmm, it's getting complicated, probably isn't worth it then.

I think it is worth cleaning up, but it probably won't be such a simple
fix. All call paths of redundant stack trace printing should be
identified and then we can decide on a clean solution.

John