linux-kernel - Re: [PATCH next v1 2/3] printk: remove safe buffers

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Message-ID: <87sg4e6lo5.fsf@jogness.linutronix.de>
Date:   Mon, 29 Mar 2021 17:10:02 +0200
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Alistair Popple <alistair@...ple.id.au>,
        Jordan Niethe <jniethe5@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Cédric Le Goater <clg@...d.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>, Yue Hu <huyue2@...ong.com>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Rafael Aquini <aquini@...hat.com>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        "Guilherme G. Piccoli" <gpiccoli@...onical.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org, kexec@...ts.infradead.org
Subject: Re: [PATCH next v1 2/3] printk: remove safe buffers

On 2021-03-29, Petr Mladek <pmladek@...e.com> wrote:
> I wonder if some console drivers rely on the fact that the write()
> callback is called with interrupts disabled.
>
> IMHO, it would be a bug when any write() callback expects that
> callers disabled the interrupts.

Agreed.

> Do you plan to remove the console-spinning stuff after offloading
> consoles to the kthreads?

Yes. Although a similar concept will be introduced to allow the threaded
printers and the atomic consoles to compete.

> Will you call console write() callback with irq enabled from the
> kthread?

No. That defeats the fundamental purpose of this entire rework
excercise. ;-)

> Anyway, we should at least add a comment why the interrupts are
> disabled.

I decided to move the local_irq_save/restore inside the console-spinning
functions and added a comment for v2.

John Ogness