drbd: Move the CREATE_BARRIER flag from connection to device

That is necessary since the whole transfer log is per connection(tconn)
and not per device(mdev).

This bug caused list corruption on the worker list. When a barrier is queued
for sending in the context of one device, another device did not see the
CREATE_BARRIER bit, and queued the same object again -> list corruption.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index e3186f2..e123406 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -320,7 +320,7 @@
 	mdev = b->w.mdev;
 
 	nob = b->next;
-	if (test_and_clear_bit(CREATE_BARRIER, &mdev->flags)) {
+	if (test_and_clear_bit(CREATE_BARRIER, &tconn->flags)) {
 		_tl_add_barrier(tconn, b);
 		if (nob)
 			tconn->oldest_tle = nob;
@@ -381,7 +381,7 @@
 				if (b->w.cb == NULL) {
 					b->w.cb = w_send_barrier;
 					inc_ap_pending(b->w.mdev);
-					set_bit(CREATE_BARRIER, &b->w.mdev->flags);
+					set_bit(CREATE_BARRIER, &tconn->flags);
 				}
 
 				drbd_queue_work(&tconn->data.work, &b->w);
@@ -448,10 +448,8 @@
  */
 void tl_clear(struct drbd_tconn *tconn)
 {
-	struct drbd_conf *mdev;
 	struct list_head *le, *tle;
 	struct drbd_request *r;
-	int vnr;
 
 	spin_lock_irq(&tconn->req_lock);
 
@@ -470,10 +468,7 @@
 	}
 
 	/* ensure bit indicating barrier is required is clear */
-	rcu_read_lock();
-	idr_for_each_entry(&tconn->volumes, mdev, vnr)
-		clear_bit(CREATE_BARRIER, &mdev->flags);
-	rcu_read_unlock();
+	clear_bit(CREATE_BARRIER, &tconn->flags);
 
 	spin_unlock_irq(&tconn->req_lock);
 }