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

[Dmitry Safonov]

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@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(-)
> 

Thanks,
          Dmitry