[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [GIT PULL] Fix lost interrupt race in Xen event channels
>>> On 30.08.10 at 10:48, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote: > Well, in 2.6.18 it was at least very unlikely that unmask_evtchn() would be > called on an already-unmasked port. And the implementation of > unmask-evtchn() is safe in the case that it is called for an > already-unmasked port -- it just does a bit more work than necessary in that > case. ... plus possibly causes an unnecessary upcall. However, do you also think that pirq_unmask_and_notify() is safe to be called twice? I would think the double EOI potentially sent to Xen could lead to an interrupt getting ack-ed that didn't even get started to be serviced yet. And this, afaict, can happen in 2.6.18 as well (ack_pirq() -> move_native_irq() -> disable_pirq()/ enable_pirq() -> pirq_unmask_and_notify() followed by end_pirq() -> pirq_unmask_and_notify()). Here, however, you couldn't even use the mask bit to detect the situation, since the masking only happens after already having called move_native_irq() (i.e. the event channel will be masked when you get into pirq_unmask_and_notify() the second time). Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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