linux-kernel - Re: [PATCH printk v3 1/7] printk: Add non-BKL (nbcon) console basic infrastructure

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Message-ID: <ZPcU96WWkDyssEie@alley>
Date:   Tue, 5 Sep 2023 13:45:59 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     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,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH printk v3 1/7] printk: Add non-BKL (nbcon) console basic
 infrastructure

On Sun 2023-09-03 17:11:33, John Ogness wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The current console/printk subsystem is protected by a Big Kernel Lock,
> (aka console_lock) which has ill defined semantics and is more or less
> stateless. This puts severe limitations on the console subsystem and
> makes forced takeover and output in emergency and panic situations a
> fragile endeavour that is based on try and pray.
> 
> The goal of non-BKL (nbcon) consoles is to break out of the console lock
> jail and to provide a new infrastructure that avoids the pitfalls and
> also allows console drivers to be gradually converted over.
> 
> The proposed infrastructure aims for the following properties:
> 
>   - Per console locking instead of global locking
>   - Per console state that allows to make informed decisions
>   - Stateful handover and takeover
> 
> As a first step, state is added to struct console. The per console state
> is an atomic_t using a 32bit bit field.
> 
> Reserve state bits, which will be populated later in the series. Wire
> it up into the console register/unregister functionality.
> 
> It was decided to use a bitfield because using a plain u32 with
> mask/shift operations resulted in uncomprehensible code.
> 
> Co-developed-by: John Ogness <john.ogness@...utronix.de>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> Signed-off-by: Thomas Gleixner (Intel) <tglx@...utronix.de>

Looks good to me:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr