IPoIB: Fix deadlock on RTNL between bcast join comp and ipoib_stop()

Taking rtnl_lock in ipoib_mcast_join_complete() causes a deadlock with
ipoib_stop().  We avoid it by scheduling the piece of code that takes
the lock on ipoib_workqueue instead of executing it directly.  This
works because we only flush the ipoib_workqueue with the RTNL not held.

The deadlock happens because ipoib_stop() calls ipoib_ib_dev_down()
which calls ipoib_mcast_dev_flush(), which calls ipoib_mcast_free(),
which calls ipoib_mcast_leave(). The latter calls
ib_sa_free_multicast(), and this waits until the multicast completion
handler finishes.  This handler is ipoib_mcast_join_complete(), which
waits for the rtnl_lock(), which was already taken by ipoib_stop().

This bug was introduced in commit a77a57a1 ("IPoIB: Fix deadlock on
RTNL in ipoib_stop()").

Signed-off-by: Yossi Etigin <yosefe@voltaire.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

3 files changed, 24 insertions, 10 deletions

diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h
index b0ffc9abe8c0..05eb41b8ab63 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib.h
+++ b/drivers/infiniband/ulp/ipoib/ipoib.h
@@ -293,6 +293,7 @@ struct ipoib_dev_priv {
 
         struct delayed_work pkey_poll_task;
         struct delayed_work mcast_task;
+        struct work_struct carrier_on_task;
         struct work_struct flush_light;
         struct work_struct flush_normal;
         struct work_struct flush_heavy;
@@ -464,6 +465,7 @@ int ipoib_dev_init(struct net_device *dev, struct ib_device *ca, int port);
 void ipoib_dev_cleanup(struct net_device *dev);
 
 void ipoib_mcast_join_task(struct work_struct *work);
+void ipoib_mcast_carrier_on_task(struct work_struct *work);
 void ipoib_mcast_send(struct net_device *dev, void *mgid, struct sk_buff *skb);
 
 void ipoib_mcast_restart_task(struct work_struct *work);
diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
index 7e9e218738fa..1b1df5cc4113 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
@@ -1075,6 +1075,7 @@ static void ipoib_setup(struct net_device *dev)
 
         INIT_DELAYED_WORK(&priv->pkey_poll_task, ipoib_pkey_poll);
         INIT_DELAYED_WORK(&priv->mcast_task,   ipoib_mcast_join_task);
+        INIT_WORK(&priv->carrier_on_task, ipoib_mcast_carrier_on_task);
         INIT_WORK(&priv->flush_light,   ipoib_ib_dev_flush_light);
         INIT_WORK(&priv->flush_normal,   ipoib_ib_dev_flush_normal);
         INIT_WORK(&priv->flush_heavy,   ipoib_ib_dev_flush_heavy);
diff --git a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
index ac33c8f3ea85..aae28620a6e5 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
@@ -366,6 +366,21 @@ static int ipoib_mcast_sendonly_join(struct ipoib_mcast *mcast)
         return ret;
 }
 
+void ipoib_mcast_carrier_on_task(struct work_struct *work)
+{
+        struct ipoib_dev_priv *priv = container_of(work, struct ipoib_dev_priv,
+                                                   carrier_on_task);
+
+        /*
+         * Take rtnl_lock to avoid racing with ipoib_stop() and
+         * turning the carrier back on while a device is being
+         * removed.
+         */
+        rtnl_lock();
+        netif_carrier_on(priv->dev);
+        rtnl_unlock();
+}
+
 static int ipoib_mcast_join_complete(int status,
                                      struct ib_sa_multicast *multicast)
 {
@@ -392,16 +407,12 @@ static int ipoib_mcast_join_complete(int status,
                                            &priv->mcast_task, 0);
                 mutex_unlock(&mcast_mutex);
 
-                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();
-                }
+                /*
+                 * Defer carrier on work to ipoib_workqueue to avoid a
+                 * deadlock on rtnl_lock here.
+                 */
+                if (mcast == priv->broadcast)
+                        queue_work(ipoib_workqueue, &priv->carrier_on_task);
 
                 return 0;
         }