linux-kernel - Re: [PATCH] printk deadlocks if called with runqueue lock held

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Date:	Fri, 18 Jan 2008 15:55:13 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Jiri Kosina <jikos@...os.cz>, LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...nvz.org>,
	Kirill Korotaev <dev@...ru>
Subject: Re: [PATCH] printk deadlocks if called with runqueue lock held

Steven Rostedt wrote:
...
> @@ -978,7 +980,13 @@ void release_console_sem(void)
>  	console_locked = 0;
>  	up(&console_sem);

Hmm, just looking at this fragment: Doesn't up() include the risk of
running onto the runqueue lock as well?

>  	spin_unlock_irqrestore(&logbuf_lock, flags);
> -	if (wake_klogd)
> +	/*
> +	 * If we try to wake up klogd while printing with the runqueue lock
> +	 * held, this will deadlock. We don't have access to the runqueue
> +	 * lock from here, but just checking for interrupts disabled
> +	 * should be enough.
> +	 */
> +	if (!irqs_disabled() && wake_klogd)
>  		wake_up_klogd();
>  }
>  EXPORT_SYMBOL(release_console_sem);

Jan
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