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Date:   Mon, 14 Feb 2022 14:35:41 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-kernel@vger.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [PATCH v3] printk: use atomic updates for klogd work
Message-ID: <YgnqLe9pWsbhV4kF@google.com>
References: <20220203112915.1350753-1-john.ogness@linutronix.de>
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 <YgUzm5POctivsjUg@alley>
 <87leyhd4wc.fsf@jogness.linutronix.de>
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On (22/02/11 12:29), 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@linutronix.de>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

FWIW
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>