To ensure that we handle all the pending interrupts (destined
for this cpu that is going down) in the interrupt subsystem
before the cpu goes offline, fixup_irqs() does:

	local_irq_enable();
	mdelay(1);
	local_irq_disable();

Enabling interrupts is not a good thing as this cpu is already
offline. So this patch replaces that logic with,

	mdelay(1);
	check APIC_IRR bits
	Retrigger the irq at the new destination if any interrupt has arrived
	via IPI.

For IO-APIC level triggered interrupts, this retrigger IPI will
appear as an edge interrupt. ack_apic_level() will detect this
condition and IO-APIC RTE's remoteIRR is cleared using directed
EOI(using IO-APIC EOI register) on Intel platforms and for
others it uses the existing mask+edge logic followed by
unmask+level.

We can also remove mdelay() and then send spuriuous interrupts
to new cpu targets for all the irqs that were handled previously
by this cpu that is going offline. While it works, I have seen
spurious interrupt messages (nothing wrong but still annoying
messages during cpu offline, which can be seen during
suspend/resume etc)
Signed-off-by: NSuresh Siddha <suresh.b.siddha@intel.com>
Acked-by: NGary Hade <garyhade@us.ibm.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
LKML-Reference: <20091026230002.043281924@sbs-t61.sc.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>