Messages in this thread | | | Date | Wed, 21 Jul 2021 16:46:21 +0200 | From | Petr Mladek <> | Subject | Re: [PATCH v2 2/2] printk: Add printk.console_verbose boot parameter |
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On Tue 2021-07-13 02:15:11, 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().
Yup, it makes sense.
> Provide printk.console_verbose boot parameter, which allows to switch off > printk being verbose on oops/panic/lockdep (making it boot parameter > instead of compile-option suggested-by Petr). > > 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> > --- > Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++ > include/linux/printk.h | 4 +++- > kernel/printk/printk.c | 6 ++++++ > 3 files changed, 18 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index bdb22006f713..9fae19b1edd8 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -4167,6 +4167,15 @@ > Format: <bool> (1/Y/y=enable, 0/N/n=disable) > default: disabled > > + printk.console_verbose= > + Raise console loglevel to highest on oops, panic or > + lockdep-detected issues (only if lock debug is on). > + With an exception to setups with low baudrate on > + serial console, keeping this enabled is a good choice > + in order to provide more debug information. > + Format: <bool> (1/Y/y=enable, 0/N/n=disable) > + default: enabled
Hmm, the name suggests that the console should always be verbose. It looks like a counterpart to the "quiet" option.
It actually is a counter part to the existing "quiet" option except that it triggers in some situations only.
Hence, I would call it "no_auto_verbose":
+ "verbose" follows the simple naming scheme of the existing "quiet" option (no "printk" and no "console" in the name)
+ "no_auto" suggests that it disables some auto-verbose behavior which is exactly what it does.
Any better idea?
> + > printk.devkmsg={on,off,ratelimit} > Control writing to /dev/kmsg. > on - unlimited logging to /dev/kmsg from userspace > diff --git a/include/linux/printk.h b/include/linux/printk.h > index a63f468a8239..9d0b8133a03c 100644 > --- a/include/linux/printk.h > +++ b/include/linux/printk.h > @@ -70,9 +70,11 @@ extern int console_printk[]; > #define minimum_console_loglevel (console_printk[2]) > #define default_console_loglevel (console_printk[3]) > > +extern bool printk_console_verbose; > + > static inline void console_verbose(void) > { > - if (console_loglevel) > + if (console_loglevel && printk_console_verbose) > console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH; > } > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 142a58d124d9..e321ee78855d 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -2404,6 +2404,12 @@ module_param_named(console_suspend, console_suspend_enabled, > MODULE_PARM_DESC(console_suspend, "suspend console during suspend" > " and hibernate operations"); > > +bool printk_console_verbose = true;
I would call it "console_auto_verbose".
> +EXPORT_SYMBOL(printk_console_verbose);
I would prefer to move console_verbose() into printk.c and export the function instead of this variable.
> +module_param_named(console_verbose, printk_console_verbose, bool, 0644); > +MODULE_PARM_DESC(console_verbose, "Raise console loglevel to highest on oops/panic/etc");
Best Regards, Petr
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