[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH] xen/events: Mask a moving irq

On 03/17/2016 12:03 PM, David Vrabel wrote:
On 17/03/16 12:45, Boris Ostrovsky wrote:
Moving an unmasked irq may result in irq handler being invoked on both
source and target CPUs.

With 2-level this can happen as follows:

On source CPU:
         evtchn_2l_handle_events() ->
             generic_handle_irq() ->
                 handle_edge_irq() ->

                        /***** WE ARE HERE *****/

                        if (VALID_EVTCHN(evtchn))

If at this moment target processor is handling an unrelated event in
evtchn_2l_handle_events()'s loop it may pick up our event since target's
cpu_evtchn_mask claims that this event belongs to it *and* the event is
unmasked and still pending. At the same time, source CPU will continue
executing its own handle_edge_irq().

With FIFO interrupt the scenario is similar: irq_move_irq() may result
in a EVTCHNOP_unmask hypercall which, in turn, may make the event
pending on the target CPU.

We can avoid this situation by moving and clearing the event while
keeping event masked.
Can you do:

    if (unlikely(irqd_is_setaffinity_pending(data))) {
        masked = test_and_set_mask()


I did think about this but then I wasn't sure whether this might open some other window for things to sneak in. It shouldn't but these things are rather subtle so I'd rather leave the order of how operations are done unchanged.

But I should indeed use irq_move_masked_irq() instead of irq_move_irq().


    } else

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.