linux-kernel - Re: [PATCH] Revert "printk: wake up all waiters"

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Message-ID: <20220526163710.0a2cd6f4@gandalf.local.home>
Date:   Thu, 26 May 2022 16:37:10 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "printk: wake up all waiters"

On Thu, 26 May 2022 22:36:56 +0206
John Ogness <john.ogness@...utronix.de> wrote:

> This reverts commit 938ba4084abcf6fdd21d9078513c52f8fb9b00d0.
> 
> The wait queue @log_wait never has exclusive waiters, so there
> is no need to use wake_up_interruptible_all(). Using
> wake_up_interruptible() was the correct function to wake all
> waiters.
> 
> Since there are no exclusive waiters, erroneously changing
> wake_up_interruptible() to wake_up_interruptible_all() did not
> result in any behavior change. However, using
> wake_up_interruptible_all() on a wait queue without exclusive
> waiters is fundamentally wrong.
> 
> Go back to using wake_up_interruptible() to wake all waiters.

(Just to show that I have been paying attention ;-)

Acked-by: Steven Rostedt (Google) <rostedt@...dmis.org>

-- Steve

> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
>  kernel/printk/printk.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index a3e1035929b0..ea3dd55709e7 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -3904,7 +3904,7 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work)
>  	}
>  
>  	if (pending & PRINTK_PENDING_WAKEUP)
> -		wake_up_interruptible_all(&log_wait);
> +		wake_up_interruptible(&log_wait);
>  }
>  
>  static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =