s390/qeth: strictly order bridge address events

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>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h
index 00ed58428163..da46af682af8 100644
--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -674,6 +674,11 @@ struct qeth_card_blkt {
 	int inter_packet_jumbo;
 };
 
+enum qeth_pnso_mode {
+	QETH_PNSO_NONE,
+	QETH_PNSO_BRIDGEPORT,
+};
+
 #define QETH_BROADCAST_WITH_ECHO    0x01
 #define QETH_BROADCAST_WITHOUT_ECHO 0x02
 struct qeth_card_info {
@@ -690,6 +695,7 @@ struct qeth_card_info {
 	/* no bitfield, we take a pointer on these two: */
 	u8 has_lp2lp_cso_v6;
 	u8 has_lp2lp_cso_v4;
+	enum qeth_pnso_mode pnso_mode;
 	enum qeth_card_types type;
 	enum qeth_link_types link_type;
 	int broadcast_capable;