On Mon, Jul 20, 2015 at 07:27:11AM +0200, Paolo Bonzini wrote: > event_notifier_test_and_clear must be called before processing events. > Otherwise, an aio_poll could "eat" the notification before the main > I/O thread invokes ppoll(). The main I/O thread then never wakes up. > This is an example of what could happen: > > i/o thread vcpu thread worker thread > --------------------------------------------------------------------- > lock_iothread > notify_me = 1 > ... > unlock_iothread > lock_iothread > notify_me = 3 > ppoll > notify_me = 1 > bh->scheduled = 1 > event_notifier_set > event_notifier_test_and_clear > ppoll > *** hang ***
I don't understand this diagram. Why is event_notifier_test_and_clear() called by the vcpu thread? event_notifier_set() was called *after* vcpu thread's ppoll() returned so I wouldn't expect the vcpu thread to see the notify. Was there a previous notify pending?
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