There is a sequence of events that can lead to a permanently masked
event channel, because xen_irq_lateeoi() is newer called. This happens
when a backend receives spurious write event from a frontend. In this
case pvcalls_conn_back_write() returns early and it does not clears the
map->write counter. As map->write > 0, pvcalls_back_ioworker() returns
without calling xen_irq_lateeoi(). This leaves the event channel in
masked state, a backend does not receive any new events from a
frontend and the whole communication stops.
Move atomic_set(&map->write, 0) to the very beginning of
pvcalls_conn_back_write() to fix this issue.
Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
Reported-by: Oleksii Moisieiev <oleksii_moisieiev@xxxxxxxx>
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