linux-kernel - Re: [PATCH 0/3] x86/dumpstack: Print registers with the same log level as the backtrace

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Message-ID: <86995860-74e7-31fb-5f94-f5b87d6aba07@arista.com>
Date:   Thu, 25 Jun 2020 17:41:23 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jann Horn <jannh@...gle.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Subject: Re: [PATCH 0/3] x86/dumpstack: Print registers with the same log
 level as the backtrace

On 6/24/20 7:50 AM, Petr Mladek wrote:
> On Tue 2020-06-23 17:29:55, Dmitry Safonov wrote:
>> show_trace_log_lvl() provides x86 platform-specific way to unwind
>> backtrace with a given log level. Unfortunately, registers dump(s) are
>> not printed with the same log level - instead, KERN_DEFAULT is always
>> used.
>>
>> Arista's switches uses quite common setup with rsyslog, where only
>> urgent messages goes to console (console_log_level=KERN_ERR), everything
>> else goes into /var/log/ as the console baud-rate often is indecently
>> slow (9600 bps).
>>
>> Backtrace dumps without registers printed have proven to be as useful as
>> morning standups. Furthermore, in order to introduce KERN_UNSUPPRESSED
>> (which I believe is still the most elegant way to fix raciness of sysrq[1])
>> the log level should be passed down the stack to register dumping
>> functions. Besides, I have a potential use-case for printing traces
>> with KERN_DEBUG level [2] (where registers dump shouldn't appear with
>> higher log level than the backtrace).
>>
>> Dmitry Safonov (3):
>>   x86/dumpstack: Add log_lvl to show_iret_regs()
>>   x86/dumpstack: Add log_lvl to __show_regs()
>>   x86/dumpstack: Show registers dump with trace's log level
> 
> The change makes sense. It is natural next step after adding log_lvl
> parameter for printing stack traces. For the entire patchset:
> 
> Acked-by: Petr Mladek <pmladek@...e.com>

I'll address the nit by Jann and resend v2 with your Ack, thanks!

> Are there any plans to add this also for other architectures, please?

Yes, I'll look into that.

Thanks,
          Dmitry