[PATCH] Fix potential interrupts during alternative patching

Interrupts must be disabled during alternative instruction patching.  On
systems with high timer IRQ rates, or when running in an emulator, timing
differences can result in random kernel panics because of running partially
patched instructions.  This doesn't yet fix NMIs, which requires extricating
the patch code from the late bug checking and is logically separate (and also
less likely to cause problems).

Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/alternative.c

@@ -344,13 +344,16 @@ void alternatives_smp_switch(int smp)
 
 void __init alternative_instructions(void)
 {
+	unsigned long flags;
 	if (no_replacement) {
 		printk(KERN_INFO "(SMP-)alternatives turned off\n");
 		free_init_pages("SMP alternatives",
 				(unsigned long)__smp_alt_begin,
 				(unsigned long)__smp_alt_end);
 		return;
 	}
+
+	local_irq_save(flags);
 	apply_alternatives(__alt_instructions, __alt_instructions_end);
 
 	/* switch to patch-once-at-boottime-only mode and free the
@@ -386,4 +389,5 @@ void __init alternative_instructions(void)
 		alternatives_smp_switch(0);
 	}
 #endif
+	local_irq_restore(flags);
 }