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

[Dmitry Safonov]

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@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
[1]: https://lore.kernel.org/lkml/20190528002412.1625-1-dima@xxxxxxxxxx/
[2]: https://lore.kernel.org/linux-doc/20190724170249.9644-1-dima@xxxxxxxxxx/
[3]: https://lore.kernel.org/lkml/20200623162958.331051-1-dima@xxxxxxxxxx/
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