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

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Date:   Wed, 31 Mar 2021 09:59:39 +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>,
        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 2021-03-30, John Ogness <john.ogness@...utronix.de> wrote:
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index e971c0a9ec9e..f090d6a1b39e 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1772,16 +1759,21 @@ static struct task_struct *console_owner;
>  static bool console_waiter;
>  
>  /**
> - * console_lock_spinning_enable - mark beginning of code where another
> + * console_lock_spinning_enable_irqsave - mark beginning of code where another
>   *	thread might safely busy wait
>   *
>   * This basically converts console_lock into a spinlock. This marks
>   * the section where the console_lock owner can not sleep, because
>   * there may be a waiter spinning (like a spinlock). Also it must be
>   * ready to hand over the lock at the end of the section.
> + *
> + * This disables interrupts because the hand over to a waiter must not be
> + * interrupted until the hand over is completed (@console_waiter is cleared).
>   */
> -static void console_lock_spinning_enable(void)
> +static void console_lock_spinning_enable_irqsave(unsigned long *flags)

I missed the prototype change for the !CONFIG_PRINTK case, resulting in:

linux/kernel/printk/printk.c:2707:3: error: implicit declaration of function ‘console_lock_spinning_enable_irqsave’; did you mean ‘console_lock_spinning_enable’? [-Werror=implicit-function-declaration]
   console_lock_spinning_enable_irqsave(&flags);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   console_lock_spinning_enable

Will be fixed for v3.

(I have now officially added !CONFIG_PRINTK to my CI tests.)

John Ogness