linux-kernel - Re: printk deadlock due to double lock attempt on current CPU's runqueue

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Message-ID: <YYwlnEQO0raDwS86@sultan-box.localdomain>
Date:   Wed, 10 Nov 2021 12:03:40 -0800
From:   Sultan Alsawaf <sultan@...neltoast.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Peter Zijlstra <peterz@...radead.org>,
        Anton Vorontsov <anton@...msg.org>,
        Ben Segall <bsegall@...gle.com>,
        Colin Cross <ccross@...roid.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        dri-devel@...ts.freedesktop.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Mel Gorman <mgorman@...e.de>, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Tony Luck <tony.luck@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>, mkoutny@...e.com
Subject: Re: printk deadlock due to double lock attempt on current CPU's
 runqueue

On Wed, Nov 10, 2021 at 11:13:37AM +0106, John Ogness wrote:
> Even after we introduce kthread printers, there will still be situations
> where direct printing is used: booting (before kthreads exist) and
> shutdown/suspend/crash situations, when the kthreads may not be
> active.

Although I'm unaware of any ongoing kthread printer work, I'm curious to know
how a kthread approach wouldn't employ a try_to_wake_up() from directly inside
printk(), since the try_to_wake_up() hit from inside the fbcon code is what
caused my deadlock.

Sultan