IPoIB: Fix multicast race between canceling and completing

ipoib_mcast_stop_thread currently tests mcast->query and if it is
NULL, does not perform wait_for_completion on the mcast and frees the
mcast object directly.

However, since both operations are done without locking, it is
possible that ipoib_mcast_join_complete is in progress on this mcast
object and has set mcast->query to NULL already.

Solve this by:
- taking priv->lock before we change mcast->query in ipoib_mcast_join_complete,
  and keeping it until we no longer need the mcast object
- taking priv->lock around mcast->query test in ipoib_mcast_stop_thread

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 12 insertions, 3 deletions

diff --git a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
index e5dc2a034530..fde442a1996d 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
@@ -437,9 +437,11 @@ static void ipoib_mcast_join_complete(int status,
         if (mcast->backoff > IPOIB_MAX_BACKOFF_SECONDS)
                 mcast->backoff = IPOIB_MAX_BACKOFF_SECONDS;
 
+        mutex_lock(&mcast_mutex);
+
+        spin_lock_irq(&priv->lock);
         mcast->query = NULL;
 
-        mutex_lock(&mcast_mutex);
         if (test_bit(IPOIB_MCAST_RUN, &priv->flags)) {
                 if (status == -ETIMEDOUT)
                         queue_work(ipoib_workqueue, &priv->mcast_task);
@@ -448,6 +450,7 @@ static void ipoib_mcast_join_complete(int status,
                                            mcast->backoff * HZ);
         } else
                 complete(&mcast->done);
+        spin_unlock_irq(&priv->lock);
         mutex_unlock(&mcast_mutex);
 
         return;
@@ -635,21 +638,27 @@ int ipoib_mcast_stop_thread(struct net_device *dev, int flush)
         if (flush)
                 flush_workqueue(ipoib_workqueue);
 
+        spin_lock_irq(&priv->lock);
         if (priv->broadcast && priv->broadcast->query) {
                 ib_sa_cancel_query(priv->broadcast->query_id, priv->broadcast->query);
                 priv->broadcast->query = NULL;
+                spin_unlock_irq(&priv->lock);
                 ipoib_dbg_mcast(priv, "waiting for bcast\n");
                 wait_for_completion(&priv->broadcast->done);
-        }
+        } else
+                spin_unlock_irq(&priv->lock);
 
         list_for_each_entry(mcast, &priv->multicast_list, list) {
+                spin_lock_irq(&priv->lock);
                 if (mcast->query) {
                         ib_sa_cancel_query(mcast->query_id, mcast->query);
                         mcast->query = NULL;
+                        spin_unlock_irq(&priv->lock);
                         ipoib_dbg_mcast(priv, "waiting for MGID " IPOIB_GID_FMT "\n",
                                         IPOIB_GID_ARG(mcast->mcmember.mgid));
                         wait_for_completion(&mcast->done);
-                }
+                } else
+                        spin_unlock_irq(&priv->lock);
         }
 
         return 0;