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

Andrew Morton
2010-03-31T20:41:52Z

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.