[PATCH 1/5] firewire: cdev: use memory barrier to access fw_device members

[Takashi Sakamoto]

The core code uses a read memory barrier when accessing the generation
and node_id members of the fw_device structure. It assumes that the
latest value of the former is visible to a processor core when the latest
value of the latter is visible, since these members are updated in reverse
order with a write memory barrier.

However, the function that fills the fw_cdev_event_bus_reset structure
does not follow this approach. Use a read memory barrier when accessing
these members.
---
 drivers/firewire/core-cdev.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index e49d8a58be09..9a3be1ceee2a 100644
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -399,18 +399,21 @@ static ssize_t fw_device_op_read(struct file *file, char __user *buffer,
 static void fill_bus_reset_event(struct fw_cdev_event_bus_reset *event,
 				 struct client *client)
 {
-	struct fw_card *card = client->device->card;
-
-	guard(spinlock_irq)(&card->lock);
-
 	event->closure	     = client->bus_reset_closure;
 	event->type          = FW_CDEV_EVENT_BUS_RESET;
+
 	event->generation    = client->device->generation;
+	smp_rmb();
 	event->node_id       = client->device->node_id;
-	event->local_node_id = card->local_node->node_id;
-	event->bm_node_id    = card->bm_node_id;
-	event->irm_node_id   = card->irm_node->node_id;
-	event->root_node_id  = card->root_node->node_id;
+
+	struct fw_card *card = client->device->card;
+
+	scoped_guard(spinlock_irq, &card->lock) {
+		event->local_node_id = card->local_node->node_id;
+		event->bm_node_id    = card->bm_node_id;
+		event->irm_node_id   = card->irm_node->node_id;
+		event->root_node_id  = card->root_node->node_id;
+	}
 }
 
 static void for_each_client(struct fw_device *device,
-- 
2.53.0