Xen devel - Oct 2010 - still lockup due to interrupt lost after backport from 2.6.31 to 2.6.32 in events.c

Hi all,

Recently i met a problem about domU lockup. i traced this problem and knew
that it may be caused by irq balancing.
>From  xen-devel community, it''s known that the workaround is to
turn off irq
balancing.
After testing , it actually worked.

However, i studied the kernel of 2.6.32 which has already fix this bug,
there''re some doubt about the difference between 2.6.32 and
2.6.31(pvops),
because after i tried to backport this patch, domU still locked up.

In my opinion , the difference is mainly in events.c, the important
difference as following:

1. void xen_evtchn_do_upcall(struct pt_regs *regs)

                               int irq = evtchn_to_irq[port];
                               struct irq_desc *desc;
+                               mask_evtchn(port);
+                               clear_evtchn(port);
+
                               if (irq != -1) {

2. static void ack_pirq(unsigned int irq)

                move_masked_irq(irq);
-                if (VALID_EVTCHN(evtchn)) {
-                        mask_evtchn(evtchn);
-                        clear_evtchn(evtchn);
-                }
+               pirq_eoi(irq);

here,  pirq_eoi ''ll be called by handle_fasteoi_irq function in
desc->chip->eoi(irq).

3. use percpu_interrupts for IPIs and VIRQs

4. use fasteoi handler for pirq ,events,msi.

*my question is how 2.6.31 drops interrupts if  migrate an irq beween vcpus
while an event is pending and what main points that 2.6.32 fixes about not
dropping are.*

i wanna know whether it matters with the advance of mask_evtchn in
*Point 1*to avoid new interrupt coming or whether it matters with eoi
called by
handle_fasteoi_irq when status is in *IRQ_INPROGRESS*.  because
handle_level_irq and handle_fasteoi_irq is almost the same except the branch
of  IRQ_INPROGRESS.  Or it matters with other points that i haven''t
find.

Deeply looking forward to your disabusing and advice.


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