Commit 10102a89 authored by Dmitry Safonov's avatar Dmitry Safonov Committed by Petr Mladek
Browse files

printk: Add printk.console_no_auto_verbose boot parameter 



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().

Provide printk.console_no_auto_verbose boot parameter, which allows
to switch off printk being verbose on oops/panic/lockdep.

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: default avatarDmitry Safonov <dima@arista.com>
Suggested-by: default avatarPetr Mladek <pmladek@suse.com>
Reviewed-by: default avatarSergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Tested-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210727130635.675184-3-dima@arista.com
parent c9110dfc

Documentation/admin-guide/kernel-parameters.txt

+9 −0
Original line number Diff line number Diff line
@@ -4101,6 +4101,15 @@ 
			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)

			default: disabled



	printk.console_no_auto_verbose=

			Disable console loglevel raise 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 0 is a good choice

			in order to provide more debug information.

			Format: <bool>

			default: 0 (auto_verbose is enabled)



	printk.devkmsg={on,off,ratelimit}

			Control writing to /dev/kmsg.

			on - unlimited logging to /dev/kmsg from userspace

include/linux/printk.h

+1 −5
Original line number Diff line number Diff line
@@ -69,11 +69,7 @@ extern int console_printk[]; 
#define minimum_console_loglevel (console_printk[2])

#define default_console_loglevel (console_printk[3])



static inline void console_verbose(void)

{

	if (console_loglevel)

		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;

}

extern void console_verbose(void);



/* strlen("ratelimit") + 1 */

#define DEVKMSG_STR_MAX_SIZE 10

kernel/printk/printk.c

+12 −0
Original line number Diff line number Diff line
@@ -2404,6 +2404,18 @@ module_param_named(console_suspend, console_suspend_enabled, 
MODULE_PARM_DESC(console_suspend, "suspend console during suspend"

	" and hibernate operations");



static bool printk_console_no_auto_verbose;



void console_verbose(void)

{

	if (console_loglevel && !printk_console_no_auto_verbose)

		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;

}

EXPORT_SYMBOL_GPL(console_verbose);



module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool, 0644);

MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");



/**

 * suspend_console - suspend the console subsystem

 *