linux-kernel - Re: [PATCH next v4 0/2] introduce printk cpu lock

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Message-ID: <YMswqJ7sV5RCxNim@alley>
Date:   Thu, 17 Jun 2021 13:23:20 +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,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Alexander Potapenko <glider@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH next v4 0/2] introduce printk cpu lock

On Thu 2021-06-17 11:56:49, John Ogness wrote:
> Hello,
> 
> While working on removing the safe buffers for printk [0] we
> stumbled on a cpu-reentrant spinning lock used by dump_stack(). This
> type of lock (dubbed a cpu lock) will cause deadlock risks once we
> introduce atomic consoles because atomic consoles also need such a
> lock.
> 
> Although we are not yet ready to introduce atomic consoles, this is
> an appropriate time to provide an official cpu lock to be used for
> all things relating to printk (including the atomic consoles, once
> they are introduced).
> 
> An example of cpu lock usage for atomic consoles can be found in the
> PREEMPT_RT tree, such as the serial8250 implementation [1] of an
> atomic console. (In PREEMPT_RT the printk cpu lock function was
> named console_atomic_lock/_unlock.)
> 
> This series is against next-20210616.
> 
> John Ogness (2):
>   lib/dump_stack: move cpu lock to printk.c
>   printk: fix cpu lock ordering

For both patches:

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

The patchset is ready for linux-next from my POV. We are getting close
to the merge window so I am going to push it tomorrow. We could always
remove it when anyone has comments the following week.

Best Regards,
Petr