From: Petr Mladek <pmladek@suse.com>
To: Dmitry Safonov <dima@arista.com>
Cc: linux-kernel@vger.kernel.org,
Dmitry Safonov <0x7f454c46@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
John Ogness <john.ogness@linutronix.de>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v2 2/2] printk: Add printk.console_verbose boot parameter
Date: Wed, 21 Jul 2021 16:46:21 +0200 [thread overview]
Message-ID: <20210721144621.ddvxouzxpp6sn4ec@pathway.suse.cz> (raw)
In-Reply-To: <20210713011511.215808-3-dima@arista.com>
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
next prev parent reply other threads:[~2021-07-21 14:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-13 1:15 [PATCH v2 0/2] printk: Add printk.console_verbose boot param Dmitry Safonov
2021-07-13 1:15 ` [PATCH v2 1/2] printk: Remove console_silent() Dmitry Safonov
2021-07-21 14:15 ` Petr Mladek
2021-07-13 1:15 ` [PATCH v2 2/2] printk: Add printk.console_verbose boot parameter Dmitry Safonov
2021-07-21 14:46 ` Petr Mladek [this message]
2021-07-26 13:37 ` Dmitry Safonov
2021-07-30 11:00 ` Petr Mladek
2021-07-30 11:01 ` [PATCH v2 0/2] printk: Add printk.console_verbose boot param Petr Mladek
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