linux-kernel - Re: [PATCH printk v2 2/5] printk: remove safe buffers

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Date:   Fri, 2 Apr 2021 11:14:18 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        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>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Nicholas Piggin <npiggin@...il.com>,
        Alistair Popple <alistair@...ple.id.au>,
        Jordan Niethe <jniethe5@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Yue Hu <huyue2@...ong.com>, Rafael Aquini <aquini@...hat.com>,
        "Guilherme G. Piccoli" <gpiccoli@...onical.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org, kexec@...ts.infradead.org
Subject: Re: [PATCH printk v2 2/5] printk: remove safe buffers

On (21/04/01 16:17), Petr Mladek wrote:
> > For the long term, we should introduce a printk-context API that allows
> > callers to perfectly pack their multi-line output into a single
> > entry. We discussed [0][1] this back in August 2020.
> 
> We need a "short" term solution. There are currently 3 solutions:
> 
> 1. Keep nmi_safe() and all the hacks around.
> 
> 2. Serialize nmi_cpu_backtrace() by a spin lock and later by
>    the special lock used also by atomic consoles.
> 
> 3. Tell complaining people how to sort the messed logs.

Are we talking about nmi_cpu_backtrace()->dump_stack() or some
other path?

dump_stack() seems to be already serialized by `dump_lock`. Hmm,
show_regs() is not serialized, seems like it should be under the
same `dump_lock` as dump_stack().