IPoIB: Fix deadlock on RTNL in ipoib_stop()

Commit c8c2afe3 ("IPoIB: Use rtnl lock/unlock when changing device
flags") added a call to rtnl_lock() in ipoib_mcast_join_task(), which
is run from the ipoib_workqueue.  However, ipoib_stop() (which is run
inside rtnl_lock()) flushes this workqueue, which leads to a deadlock
if the join task is pending.

Fix this by simply not flushing the workqueue from ipoib_stop().  It
turns out that we really don't care about workqueue tasks running
during or after ipoib_stop(), as long as we make sure to flush the
workqueue before unregistering a netdev.

This fixes <https://bugs.openfabrics.org/show_bug.cgi?id=1114>.

Signed-off-by: Roland Dreier <rolandd@cisco.com>

2 files changed, 18 insertions, 11 deletions

diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
index f51201b17bfd..7e9e218738fa 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
@@ -156,14 +156,8 @@ static int ipoib_stop(struct net_device *dev)
 
         netif_stop_queue(dev);
 
-        /*
-         * Now flush workqueue to make sure a scheduled task doesn't
-         * bring our internal state back up.
-         */
-        flush_workqueue(ipoib_workqueue);
-
-        ipoib_ib_dev_down(dev, 1);
-        ipoib_ib_dev_stop(dev, 1);
+        ipoib_ib_dev_down(dev, 0);
+        ipoib_ib_dev_stop(dev, 0);
 
         if (!test_bit(IPOIB_FLAG_SUBINTERFACE, &priv->flags)) {
                 struct ipoib_dev_priv *cpriv;
@@ -1314,7 +1308,7 @@ sysfs_failed:
 
 register_failed:
         ib_unregister_event_handler(&priv->event_handler);
-        flush_scheduled_work();
+        flush_workqueue(ipoib_workqueue);
 
 event_failed:
         ipoib_dev_cleanup(priv->dev);
@@ -1373,7 +1367,12 @@ static void ipoib_remove_one(struct ib_device *device)
 
         list_for_each_entry_safe(priv, tmp, dev_list, list) {
                 ib_unregister_event_handler(&priv->event_handler);
-                flush_scheduled_work();
+
+                rtnl_lock();
+                dev_change_flags(priv->dev, priv->dev->flags & ~IFF_UP);
+                rtnl_unlock();
+
+                flush_workqueue(ipoib_workqueue);
 
                 unregister_netdev(priv->dev);
                 ipoib_dev_cleanup(priv->dev);
diff --git a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
index 8950e9546f4e..ac33c8f3ea85 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
@@ -392,8 +392,16 @@ static int ipoib_mcast_join_complete(int status,
                                            &priv->mcast_task, 0);
                 mutex_unlock(&mcast_mutex);
 
-                if (mcast == priv->broadcast)
+                if (mcast == priv->broadcast) {
+                        /*
+                         * Take RTNL lock here to avoid racing with
+                         * ipoib_stop() and turning the carrier back
+                         * on while a device is being removed.
+                         */
+                        rtnl_lock();
                         netif_carrier_on(dev);
+                        rtnl_unlock();
+                }
 
                 return 0;
         }