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

[Linus Torvalds]

On Thu, 17 Jan 2008, Steven Rostedt wrote:
>
> Calling printk with interrupts disabled should only be done for
> emergencies and debugging anyway.

Agreed, I think this is sane.

> And with this patch, my code ran fine ;-)

Patch looks fine, but I'm saddened:

> +	/*
> +	 * 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();

..because we actually *have* the old hardware irq enable/disable value in 
in that "flags" parameter we just restored, so it's more than a bit sad to 
then ask again whether they were disabled or not!

IOW, I think this should be

	if (raw_irqs_disabled_flags(flags) && wake_klogd)
		wake_up_klogd();

Of course, not all architectures seem to suport that thing (it's currently 
only used by the CONFIG_TRACE_IRQFLAGS config option).

Damn. So close, yet so far away.

			Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/