IB/core: Let IB core distribute cache update events

Currently when the low level driver notifies Pkey, GID, and port change
events they are notified to the registered handlers in the order they are
registered.

IB core and other ULPs such as IPoIB are interested in GID, LID, Pkey
change events.

Since all GID queries done by ULPs are serviced by IB core, and the IB
core deferes cache updates to a work queue, it is possible for other
clients to see stale cache data when they handle their own events.

For example, the below call tree shows how ipoib will call
rdma_query_gid() concurrently with the update to the cache sitting in the
WQ.

mlx5_ib_handle_event()
  ib_dispatch_event()
    ib_cache_event()
       queue_work() -> slow cache update

    [..]
    ipoib_event()
     queue_work()
       [..]
       work handler
         ipoib_ib_dev_flush_light()
           __ipoib_ib_dev_flush()
              ipoib_dev_addr_changed_valid()
                rdma_query_gid() <- Returns old GID, cache not updated.

Move all the event dispatch to a work queue so that the cache update is
always done before any clients are notified.

Fixes: f35faa4ba956 ("IB/core: Simplify ib_query_gid to always refer to cache")
Link: https://lore.kernel.org/r/20191212113024.336702-3-leon@kernel.org
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 10 insertions, 23 deletions

diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
index 84dd74fe13b8..c38b2b0b078a 100644
--- a/drivers/infiniband/core/device.c
+++ b/drivers/infiniband/core/device.c
@@ -588,6 +588,7 @@ struct ib_device *_ib_alloc_device(size_t size)
 
 	INIT_LIST_HEAD(&device->event_handler_list);
 	spin_lock_init(&device->event_handler_lock);
+	init_rwsem(&device->event_handler_rwsem);
 	mutex_init(&device->unregistration_lock);
 	/*
 	 * client_data needs to be alloc because we don't want our mark to be
@@ -1931,17 +1932,15 @@ EXPORT_SYMBOL(ib_set_client_data);
  *
  * ib_register_event_handler() registers an event handler that will be
  * called back when asynchronous IB events occur (as defined in
- * chapter 11 of the InfiniBand Architecture Specification).  This
- * callback may occur in interrupt context.
+ * chapter 11 of the InfiniBand Architecture Specification). This
+ * callback occurs in workqueue context.
  */
 void ib_register_event_handler(struct ib_event_handler *event_handler)
 {
-	unsigned long flags;
-
-	spin_lock_irqsave(&event_handler->device->event_handler_lock, flags);
+	down_write(&event_handler->device->event_handler_rwsem);
 	list_add_tail(&event_handler->list,
 		      &event_handler->device->event_handler_list);
-	spin_unlock_irqrestore(&event_handler->device->event_handler_lock, flags);
+	up_write(&event_handler->device->event_handler_rwsem);
 }
 EXPORT_SYMBOL(ib_register_event_handler);
 
@@ -1954,35 +1953,23 @@ EXPORT_SYMBOL(ib_register_event_handler);
  */
 void ib_unregister_event_handler(struct ib_event_handler *event_handler)
 {
-	unsigned long flags;
-
-	spin_lock_irqsave(&event_handler->device->event_handler_lock, flags);
+	down_write(&event_handler->device->event_handler_rwsem);
 	list_del(&event_handler->list);
-	spin_unlock_irqrestore(&event_handler->device->event_handler_lock, flags);
+	up_write(&event_handler->device->event_handler_rwsem);
 }
 EXPORT_SYMBOL(ib_unregister_event_handler);
 
-/**
- * ib_dispatch_event - Dispatch an asynchronous event
- * @event:Event to dispatch
- *
- * Low-level drivers must call ib_dispatch_event() to dispatch the
- * event to all registered event handlers when an asynchronous event
- * occurs.
- */
-void ib_dispatch_event(struct ib_event *event)
+void ib_dispatch_event_clients(struct ib_event *event)
 {
-	unsigned long flags;
 	struct ib_event_handler *handler;
 
-	spin_lock_irqsave(&event->device->event_handler_lock, flags);
+	down_read(&event->device->event_handler_rwsem);
 
 	list_for_each_entry(handler, &event->device->event_handler_list, list)
 		handler->handler(handler, event);
 
-	spin_unlock_irqrestore(&event->device->event_handler_lock, flags);
+	up_read(&event->device->event_handler_rwsem);
 }
-EXPORT_SYMBOL(ib_dispatch_event);
 
 static int iw_query_port(struct ib_device *device,
 			   u8 port_num,