linux-kernel - Re: [PATCH v2 0/3] x86/dumpstack: Print registers with the same log level as the backtrace

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Message-ID: <a6a9072f-8b8c-1b86-4f01-af254d968811@arista.com>
Date:   Mon, 20 Jul 2020 19:51:51 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Jann Horn <jannh@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH v2 0/3] x86/dumpstack: Print registers with the same log
 level as the backtrace

Hi Ingo, Thomas,

Could you take these to x86/tip tree?
(in case they are good enough)

On 6/29/20 3:48 PM, Dmitry Safonov wrote:
> Changes since v1 [3]:
> - Use (enum show_regs_mode) instead of (int) [nit by Jann, thanks!]
> - Add acks from Petr
> 
> 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).
> 
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Petr Mladek <pmladek@...e.com>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: x86@...nel.org
> [1]: https://lore.kernel.org/lkml/20190528002412.1625-1-dima@arista.com/
> [2]: https://lore.kernel.org/linux-doc/20190724170249.9644-1-dima@arista.com/
> [3]: https://lore.kernel.org/lkml/20200623162958.331051-1-dima@arista.com/
> 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
> 
>  arch/x86/include/asm/kdebug.h |  5 ++--
>  arch/x86/kernel/dumpstack.c   | 23 +++++++++-------
>  arch/x86/kernel/process_32.c  | 29 ++++++++++----------
>  arch/x86/kernel/process_64.c  | 51 ++++++++++++++++++-----------------
>  4 files changed, 57 insertions(+), 51 deletions(-)
> 

Thanks,
          Dmitry