linux-kernel - Re: [PATCH v2] printk: defer_console

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Message-ID: <YgUzm5POctivsjUg@alley>
Date:   Thu, 10 Feb 2022 16:47:39 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH v2] printk: defer_console_output: use atomic update

On Mon 2022-02-07 10:52:20, John Ogness wrote:
> The per-cpu @printk_pending variable can be updated from
> sleepable contexts, such as:
> 
>   get_random_bytes()
>     warn_unseeded_randomness()
>       printk_deferred()
>         defer_console_output()
> 
> and can be updated from interrupt contexts, such as:
> 
>   handle_irq_event_percpu()
>     __irq_wake_thread()
>       wake_up_process()
>         try_to_wake_up()
>           select_task_rq()
>             select_fallback_rq()
>               printk_deferred()
>                 defer_console_output()
> 
> and can be updated from NMI contexts, such as:
> 
>   vprintk()
>     if (in_nmi()) defer_console_output()
> 
> Therefore this_cpu_or(), the atomic variant of __this_cpu_or(),
> should be used to update the variable.
> 
> Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

Makes sense.

The patch has been committed into printk/linux.git, branch for-5.18.

Best Regards,
Petr