From: Dmitry Safonov Date: Tue, 27 Jul 2021 13:06:35 +0000 (+0100) Subject: printk: Add printk.console_no_auto_verbose boot parameter X-Git-Tag: v5.15-rc1~136^2~2^2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=10102a890b543a8a08457dc69fa55bc032403c7d;p=thirdparty%2Flinux.git 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 Cc: John Ogness Cc: Petr Mladek Cc: Sergey Senozhatsky Cc: Steven Rostedt Signed-off-by: Dmitry Safonov Suggested-by: Petr Mladek Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek Tested-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210727130635.675184-3-dima@arista.com --- diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 26453f250683d..fdd80888217a1 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4101,6 +4101,15 @@ Format: (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: + default: 0 (auto_verbose is enabled) + 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 f3f1a1eb19bdc..a5e1c5adfc3fb 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -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 diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 142a58d124d95..a6b94c3c5ac54 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -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 *