IRQs without IRQF_DISABLED could nest to arbitrary level.

At worst this would mean having as many IRQ handlers stack frames, as there
are interrupts registered --- enough to cause a stack overflow.

This patch makes a limit to have at most two handlers on the stack.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Index: linux-2.6.26-rc5-devel/include/linux/interrupt.h
===================================================================
--- linux-2.6.26-rc5-devel.orig/include/linux/interrupt.h	2008-06-20 23:34:04.000000000 +0200
+++ linux-2.6.26-rc5-devel/include/linux/interrupt.h	2008-06-20 23:36:03.000000000 +0200
@@ -95,7 +95,7 @@
 #ifdef CONFIG_LOCKDEP
 # define local_irq_enable_in_hardirq()	do { } while (0)
 #else
-# define local_irq_enable_in_hardirq()	local_irq_enable()
+# define local_irq_enable_in_hardirq()	do { if (hardirq_count() <= (1 << HARDIRQ_SHIFT)) local_irq_enable(); } while (0)
 #endif
 
 extern void disable_irq_nosync(unsigned int irq);