From: Petr Mladek <pmladek@suse.com>
To: David Laight <David.Laight@aculab.com>
Cc: John Ogness <john.ogness@linutronix.de>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>,
Corey Minyard <cminyard@mvista.com>,
Kees Cook <keescook@chromium.org>,
Christian Brauner <christian.brauner@ubuntu.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
Mark Brown <broonie@kernel.org>,
Josef Bacik <josef@toxicpanda.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Shawn Guo <shawn.guo@linaro.org>,
Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>,
Andrew Morton <akpm@linux-foundation.org>,
Wang Qing <wangqing@vivo.com>, Tejun Heo <tj@kernel.org>,
Randy Dunlap <rdunlap@infradead.org>,
Alexander Potapenko <glider@google.com>,
Stephen Boyd <sboyd@kernel.org>,
Nicholas Piggin <npiggin@gmail.com>,
"rcu@vger.kernel.org" <rcu@vger.kernel.org>
Subject: Re: [PATCH printk v1 09/13] printk: add functions to allow direct printing
Date: Fri, 18 Feb 2022 13:52:23 +0100 [thread overview]
Message-ID: <Yg+Wh45hckprBxdp@alley> (raw)
In-Reply-To: <ca5b7ec96aa444c292b3413a6374028b@AcuMS.aculab.com>
On Fri 2022-02-18 09:00:46, David Laight wrote:
> > On Mon 2022-02-07 20:49:19, John Ogness wrote:
> > > Once kthread printing is introduced, console printing will no longer
> > > occur in the context of the printk caller. However, there are some
> > > special contexts where it is desirable for the printk caller to
> > > directly print out kernel messages.
>
> Yes - most of them.
>
> It is going to be pretty impossible to do 'hard' kernel debugging
> if printk get deferred.
What do you exactly mean by 'hard' kernel debugging, please?
What exactly won't be possible, please?
It is really important to talk about real scenarios because we
do our best to address them. This patchset disables the deferred
console handling in several situations, especially during panic,
reboot, kexec. The consoles are flushed during suspend, etc.
The patchset solves real problems, soft and live-lockups and even
deadlocks.
It will actually allow debugging when too many messages caused
softlockups and the system died. I saw it many times during boot
of systems with many network interfaces or disks. Backtraces
from all CPUs and processes, detailed Oops reports, and similar
extensive output was able to kill the system.
In each case, the legacy "direct" mode will still be around.
> Typically there already is a deferral method.
> The prints aren't done by the kernel, but by syslogd.
syslogd helps only when userspace works and the messages
can be stored on a filesystems.
And it is perfectly fine and much more safe to defer consoles
most of the time. I have seen many reports where consoles put
the system into knees. And sometime printk() was the root of all
problems.
Best Regards,
Petr
next prev parent reply other threads:[~2022-02-18 12:52 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-07 19:43 [PATCH printk v1 00/13] implement threaded console printing John Ogness
2022-02-07 19:43 ` [PATCH printk v1 01/13] printk: rename cpulock functions John Ogness
2022-02-11 12:44 ` Petr Mladek
2022-02-11 14:42 ` John Ogness
2022-02-11 20:57 ` Steven Rostedt
2022-02-11 21:04 ` Peter Zijlstra
2022-02-15 9:32 ` Petr Mladek
2022-02-15 9:13 ` Petr Mladek
2022-02-14 6:49 ` Sergey Senozhatsky
2022-02-14 9:45 ` John Ogness
2022-02-15 9:29 ` Petr Mladek
2022-02-16 3:27 ` Sergey Senozhatsky
2022-02-17 14:34 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 02/13] printk: cpu sync always disable interrupts John Ogness
2022-02-11 12:58 ` Petr Mladek
2022-02-14 6:36 ` Sergey Senozhatsky
2022-02-07 19:43 ` [PATCH printk v1 03/13] printk: use percpu flag instead of cpu_online() John Ogness
2022-02-11 16:05 ` Petr Mladek
2022-02-14 7:08 ` Sergey Senozhatsky
2022-02-14 7:35 ` Sergey Senozhatsky
2022-02-15 10:38 ` Petr Mladek
2022-02-16 3:29 ` Sergey Senozhatsky
2022-03-02 14:21 ` John Ogness
2022-03-04 15:56 ` Petr Mladek
2022-03-05 17:05 ` Jason A. Donenfeld
2022-03-07 16:14 ` Petr Mladek
2022-02-16 13:58 ` two locations: was: " Petr Mladek
2022-03-02 14:49 ` John Ogness
2022-03-04 16:14 ` Petr Mladek
2022-03-07 10:06 ` John Ogness
2022-03-08 16:08 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 04/13] printk: get caller_id/timestamp after migration disable John Ogness
2022-02-15 5:53 ` Sergey Senozhatsky
2022-02-15 11:56 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 05/13] printk: call boot_delay_msec() in printk_delay() John Ogness
2022-02-15 5:58 ` Sergey Senozhatsky
2022-02-15 14:59 ` Petr Mladek
2022-02-16 3:21 ` Sergey Senozhatsky
2022-02-15 15:03 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 06/13] printk: refactor and rework printing logic John Ogness
2022-02-16 15:43 ` Petr Mladek
2022-03-02 16:10 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 07/13] printk: move buffer definitions into console_emit_next_record() caller John Ogness
2022-02-16 16:10 ` Petr Mladek
2022-03-02 16:25 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 08/13] printk: add pr_flush() John Ogness
2022-02-17 10:11 ` Petr Mladek
2022-03-02 17:23 ` John Ogness
2022-03-04 13:24 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 09/13] printk: add functions to allow direct printing John Ogness
2022-02-17 12:52 ` Petr Mladek
2022-02-18 9:00 ` David Laight
2022-02-18 12:52 ` Petr Mladek [this message]
2022-03-03 14:37 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 10/13] printk: add kthread console printers John Ogness
2022-02-18 9:00 ` early start: was: " Petr Mladek
2022-02-18 9:04 ` start&stop: " Petr Mladek
2022-02-18 9:08 ` main loop: " Petr Mladek
2022-02-18 9:12 ` wake_up_all: " Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 11/13] printk: reimplement console_lock for proper kthread support John Ogness
2022-02-18 16:20 ` Petr Mladek
2022-02-18 21:41 ` John Ogness
2022-02-18 22:03 ` John Ogness
2022-02-22 11:42 ` Petr Mladek
2022-02-23 17:20 ` John Ogness
2022-02-24 8:27 ` Petr Mladek
2022-02-23 10:19 ` Petr Mladek
2022-03-09 13:56 ` John Ogness
2022-03-10 14:34 ` Petr Mladek
2022-03-10 16:08 ` John Ogness
2022-03-11 10:26 ` Petr Mladek
2022-03-11 13:28 ` John Ogness
2022-03-11 16:17 ` Petr Mladek
2022-03-11 22:21 ` John Ogness
2022-03-14 14:08 ` Petr Mladek
2022-03-14 14:43 ` John Ogness
2022-03-14 15:53 ` Petr Mladek
2022-03-11 18:41 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 12/13] printk: remove @console_locked John Ogness
2022-02-23 12:17 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 13/13] console: introduce CON_MIGHT_SLEEP for vt John Ogness
2022-02-23 13:37 ` Petr Mladek
2022-02-23 18:31 ` Greg Kroah-Hartman
[not found] ` <20220208083620.2736-1-hdanton@sina.com>
2022-02-08 11:08 ` [PATCH printk v1 10/13] printk: add kthread console printers John Ogness
2022-02-08 14:53 ` Petr Mladek
2022-02-14 6:12 ` Sergey Senozhatsky
2022-02-14 10:02 ` Petr Mladek
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