linux-kernel - Re: [PATCH printk 10/18] kgbd: Pretend that console list walk is safe

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Message-ID: <87o7uxugbr.fsf@jogness.linutronix.de>
Date:   Fri, 30 Sep 2022 15:50:56 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>,
        Doug Anderson <dianders@...omium.org>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Aaron Tomlin <atomlin@...hat.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-serial@...r.kernel.org
Subject: Re: [PATCH printk 10/18] kgbd: Pretend that console list walk is safe

On 2022-09-30, Petr Mladek <pmladek@...e.com> wrote:
> Anyway, what about using the later added SRCU walk here?
> After all, this is exactly what RCU is for, isn't it?

So I think a lot of the problems with this series is that SRCU is
introduced too late. We are debating things in patch 6 that are
irrelevant by patch 12.

I will rework the series so that the changes come in the following
order:

1. provide an atomic console_is_enabled()

2. convert the list to SRCU

3. move all iterators from console_lock()/console_trylock() to SRCU

Step 3 may result in console_lock()/console_trylock() calls disappearing
or relocating to where they are needed for non-list-synchronization
purposes.

John