linux-kernel - Re: [PATCH v3] printk: use atomic updates for klogd work

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Message-ID: <YgvGQO+RbPQ/PEEq@alley>
Date:   Tue, 15 Feb 2022 16:26:56 +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 v3] printk: use atomic updates for klogd work

On Fri 2022-02-11 12:29:37, 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 the atomic variant of the updating functions must be used.
> 
> Replace __this_cpu_xchg() with this_cpu_xchg().
> Replace __this_cpu_or() with this_cpu_or().
> 
> Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

The v3 patch is comitted in printk/linux.git, branch for.5.18.

I have replaced v2 version with it.

Best Regards,
Petr