The current code for bridge address events has two shortcomings in its
control sequence:
1. after disabling address events via PNSO, we don't flush the remaining
events from the event_wq. So if the feature is re-enabled fast
enough, stale events could leak over.
2. PNSO and the events' arrival via the READ ccw device are unordered.
So even if we flushed the workqueue, it's difficult to say whether
the READ device might produce more events onto the workqueue
afterwards.
Fix this by
1. explicitly fencing off the events when we no longer care, in the
READ device's event handler. This ensures that once we flush the
workqueue, it doesn't get additional address events.
2. Flush the workqueue after disabling the events & fencing them off.
As the code that triggers the flush will typically hold the sbp_lock,
we need to rework the worker code to avoid a deadlock here in case
of a 'notifications-stopped' event. In case of lock contention,
requeue such an event with a delay. We'll eventually aquire the lock,
or spot that the feature has been disabled and the event can thus be
discarded.
This leaves the theoretical race that a stale event could arrive
_after_ we re-enabled ourselves to receive events again. Such an event
would be impossible to distinguish from a 'good' event, nothing we can
do about it.
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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