Messages in this thread | | | Date | Fri, 25 Jun 2021 11:13:06 +0200 | From | Petr Mladek <> | Subject | Re: [PATCH] printk: Add CONFIG_CONSOLE_LOGLEVEL_PANIC |
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On Tue 2021-06-22 15:33:50, Dmitry Safonov wrote: > console_verbose() increases console loglevel to CONSOLE_LOGLEVEL_MOTORMOUTH, > which provides more information to debug a panic/oops. > > Unfortunately, in Arista we maintain some DUTs (Device Under Test) that > are configured to have 9600 baud rate. While verbose console messages > have their value to post-analyze crashes, on such setup they: > - may prevent panic/oops messages being printed > - take too long to flush on console resulting in watchdog reboot > > In all our setups we use kdump which saves dmesg buffer after panic, > so in reality those extra messages on console provide no additional value, > but rather add risk of not getting to __crash_kexec().
It makes sense.
> Provide CONFIG_CONSOLE_LOGLEVEL_PANIC, which allows to choose how > verbose the kernel must be on oops/panic. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: John Ogness <john.ogness@linutronix.de> > Cc: Petr Mladek <pmladek@suse.com> > Cc: Sergey Senozhatsky <senozhatsky@chromium.org> > Cc: Steven Rostedt <rostedt@goodmis.org> > Signed-off-by: Dmitry Safonov <dima@arista.com> > --- > include/linux/printk.h | 4 ++-- > lib/Kconfig.debug | 13 +++++++++++++ > 2 files changed, 15 insertions(+), 2 deletions(-) > > diff --git a/include/linux/printk.h b/include/linux/printk.h > index fe7eb2351610..5a65a719f917 100644 > --- a/include/linux/printk.h > +++ b/include/linux/printk.h > @@ -76,8 +76,8 @@ static inline void console_silent(void) > > static inline void console_verbose(void) > { > - if (console_loglevel) > - console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH; > + if (console_loglevel && (CONFIG_CONSOLE_LOGLEVEL_PANIC > 0)) > + console_loglevel = CONFIG_CONSOLE_LOGLEVEL_PANIC;
console_verbose() is called also in some other situations. For example, check_hung_task(), oops_begin(), debug_locks_ff(). These do not always lead to panic.
At minimum, the name is misleading. It should be something like CONFIG_CONSOLE_LOGLEVEL_VERBOSE.
But the question is whether we really want to limit the loglevel also in the non-panic scenarios. IMHO, it is a bad idea.
A better solution would be to introduce console_verbose_panic() and use it only when it is really going to panic. The function should also use the lower value only when crash dump is really successfully enabled.
> } > > /* strlen("ratelimit") + 1 */ > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index 678c13967580..0c12cafd9d8b 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -61,6 +61,19 @@ config CONSOLE_LOGLEVEL_QUIET > will be used as the loglevel. IOW passing "quiet" will be the > equivalent of passing "loglevel=<CONSOLE_LOGLEVEL_QUIET>" > > +config CONSOLE_LOGLEVEL_PANIC > + int "panic console loglevel (1-15)"
The range is 1-15 here.
> + range 0 15
But it is 0-15 here. If you use "range 1 15" you should not need the check (CONFIG_CONSOLE_LOGLEVEL_PANIC > 0) in the code.
> + default "15" > + help > + loglevel to use in kernel panic or oopses. > + > + Usually in order to provide more debug information on console upon > + panic, one wants to see everything being printed (loglevel = 15). > + With an exception to setups with low baudrate on serial console, > + keeping this value high is a good choice. > + 0 value is to keep the loglevel during panic/oops unchanged.
The trick with 0 value just makes things more complicated. The default "15" does the same job and should be good enough. The hard-coded default is good enough for the other CONSOLE_LOGLEVEL_* settings.
Best Regards, Petr
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