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

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Message-Id: <20200629144847.492794-1-dima@arista.com>
Date:   Mon, 29 Jun 2020 15:48:44 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.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>, Petr Mladek <pmladek@...e.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: [PATCH v2 0/3] x86/dumpstack: Print registers with the same log level as the backtrace

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(-)

-- 
2.27.0