[patch] setup_boot_APIC_clock() irq-enable fix

[Ingo Molnar <mingo@elte.hu>]

* Michal Piotrowski <michal.k.k.piotrowski@gmail.com> wrote:

> Hi Ingo,

> 2.6.21-rc4-rt0

> BUG: at kernel/fork.c:1033 copy_process()

thanks Michal - this is a real bug that affects upstream too. Find the 
fix below - i've test-booted it and it fixes the warning.

Linus, Andrew, this is a must-have for v2.6.21.

	Ingo

--------------->
Subject: [patch] setup_boot_APIC_clock() irq-enable fix
From: Ingo Molnar <mingo@elte.hu>

latest -git triggers an irqtrace/lockdep warning of a leaked
irqs-off condition:

  BUG: at kernel/fork.c:1033 copy_process()

after some debugging it turns out that commit ca1b940c accidentally left 
interrupts disabled - which trickled down all the way to the first time 
we fork a kernel thread and triggered the warning.

the fix is to re-enable interrupts in the 'else' branch of 
setup_boot_APIC_clock()'s pmtimers calibration path.

Reported-by: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/i386/kernel/apic.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux/arch/i386/kernel/apic.c
===================================================================
--- linux.orig/arch/i386/kernel/apic.c
+++ linux/arch/i386/kernel/apic.c
@@ -507,7 +507,8 @@ void __init setup_boot_APIC_clock(void)
 			apic_printk(APIC_VERBOSE, "... jiffies result ok\n");
 		else
 			local_apic_timer_verify_ok = 0;
-	}
+	} else
+		local_irq_enable();
 
 	if (!local_apic_timer_verify_ok) {
 		printk(KERN_WARNING