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printk: Add printk.console_no_auto_verbose boot parameter

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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: Dmitry Safonov <dima@arista.com>
Suggested-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210727130635.675184-3-dima@arista.com
This commit is contained in:
Dmitry Safonov 2021-07-27 14:06:35 +01:00 committed by Petr Mladek
parent c9110dfcfc
commit 10102a890b
3 changed files with 22 additions and 5 deletions
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9
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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

6
include/linux/printk.h
View File

@ -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

12
kernel/printk/printk.c
View File

@ -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
*