linux-kernel - Re: [RFC V2 12/21] rv/reactor: Add the printk reactor

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Message-ID: <87r1842r1m.fsf@jogness.linutronix.de>
Date:   Tue, 15 Feb 2022 14:39:09 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Gabriele Paoloni <gpaoloni@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-trace-devel@...r.kernel.org
Subject: Re: [RFC V2 12/21] rv/reactor: Add the printk reactor

On 2022-02-15, Daniel Bristot de Oliveira <bristot@...nel.org> wrote:
>> I suggest using printk_deferred() for this reactor for now. With
>> printk_deferred() the message and timestamp are immediately and
>> locklessly stored in the buffer, and the printing is performed in a
>> separate context. printk_deferred() is safe for all contexts.
>
> Question: Does it always postpone or only postpone when in a
> particular contexts, like, with irqs disabled?

printk_deferred() always postpones printing.

> Note: do not use this reactor with rq_lock taken, it will lock the
> system until printk can handle that.

Perhaps you could explain thi comment in your commit message?  printk()
should never lock the system.

John