linux-kernel - RE: [PATCH printk v1 09/13] printk: add functions to allow direct printing

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Date:   Fri, 18 Feb 2022 09:00:46 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Petr Mladek' <pmladek@...e.com>,
        John Ogness <john.ogness@...utronix.de>
CC:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Josh Triplett" <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Corey Minyard <cminyard@...sta.com>,
        Kees Cook <keescook@...omium.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Mark Brown <broonie@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Shawn Guo" <shawn.guo@...aro.org>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wang Qing <wangqing@...o.com>, Tejun Heo <tj@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Alexander Potapenko <glider@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>
Subject: RE: [PATCH printk v1 09/13] printk: add functions to allow direct
 printing

> 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.

Typically there already is a deferral method.
The prints aren't done by the kernel, but by syslogd.

	David

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