Re: start_kernel(): bug: interrupts were enabled early

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 26 Mar 2010 01:11:00 +0530
Rabin Vincent <rabin@rab.in> wrote:

> On latest git, I'm seeing "start_kernel(): bug: interrupts were enabled
> early" messages on ARM (sample log below).
> 
> This appears to be caused by:
> 
>   start_kernel -> radix_tree_init -> kmem_cache_create (slub) ->
>    down_write -> __down_write (lib/rwsem-spinlock.c) -> spin_unlock_irq
> 
> radix_tree_init was moved earlier by:
> 
>   commit 773e3eb7b81e5ba13b5155dfb3bb75b8ce37f8f9
>   Author: Yinghai Lu <yinghai@kernel.org>
>   Date:   Wed Feb 10 01:20:33 2010 -0800
> 
>       init: Move radix_tree_init() early
> 
>       Prepare for using radix trees in early_irq_init().
> 
>       Signed-off-by: Yinghai Lu <yinghai@kernel.org>
>       LKML-Reference: <1265793639-15071-30-git-send-email-yinghai@kernel.org>
>       Signed-off-by: H. Peter Anvin <hpa@zytor.com>
> 

That's going to be hard to fix.

Once upon a time, enabling interrupts too early in boot would kill
powerpc boxes stone dead.  From the lack of noise I assume that this is
not happening in current kernels for some reason.

We have two checks in start_kernel():

	if (!irqs_disabled()) {
		printk(KERN_WARNING "start_kernel(): bug: interrupts were "
				"enabled *very* early, fixing it\n");
		local_irq_disable();
	}
	rcu_init();
	radix_tree_init();
	/* init some links before init_ISA_irqs() */
	early_irq_init();
	init_IRQ();
	prio_tree_init();
	init_timers();
	hrtimers_init();
	softirq_init();
	timekeeping_init();
	time_init();
	profile_init();
	if (!irqs_disabled())
		printk(KERN_CRIT "start_kernel(): bug: interrupts were "
				 "enabled early\n");

perhaps the second one isn't needed?  Perhaps no architecture requires
that local interrupts be disabled across the above initialisations?


I'll ask Rafael and Maciej to track this as a post-2.6.33 regression.