IB: refcount race fixes

Fix race condition during destruction calls to avoid possibility of
accessing object after it has been freed.  Instead of waking up a wait
queue directly, which is susceptible to a race where the object is
freed between the reference count going to 0 and the wake_up(), use a
completion to wait in the function doing the freeing.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 25 insertions, 22 deletions

diff --git a/drivers/infiniband/core/mad.c b/drivers/infiniband/core/mad.c
index 469b6923a2e..5ad41a64314 100644
--- a/drivers/infiniband/core/mad.c
+++ b/drivers/infiniband/core/mad.c
@@ -352,7 +352,7 @@ struct ib_mad_agent *ib_register_mad_agent(struct ib_device *device,
         INIT_WORK(&mad_agent_priv->local_work, local_completions,
                    mad_agent_priv);
         atomic_set(&mad_agent_priv->refcount, 1);
-        init_waitqueue_head(&mad_agent_priv->wait);
+        init_completion(&mad_agent_priv->comp);
 
         return &mad_agent_priv->agent;
 
@@ -467,7 +467,7 @@ struct ib_mad_agent *ib_register_mad_snoop(struct ib_device *device,
         mad_snoop_priv->agent.qp = port_priv->qp_info[qpn].qp;
         mad_snoop_priv->agent.port_num = port_num;
         mad_snoop_priv->mad_snoop_flags = mad_snoop_flags;
-        init_waitqueue_head(&mad_snoop_priv->wait);
+        init_completion(&mad_snoop_priv->comp);
         mad_snoop_priv->snoop_index = register_snoop_agent(
                                                 &port_priv->qp_info[qpn],
                                                 mad_snoop_priv);
@@ -486,6 +486,18 @@ error1:
 }
 EXPORT_SYMBOL(ib_register_mad_snoop);
 
+static inline void deref_mad_agent(struct ib_mad_agent_private *mad_agent_priv)
+{
+        if (atomic_dec_and_test(&mad_agent_priv->refcount))
+                complete(&mad_agent_priv->comp);
+}
+
+static inline void deref_snoop_agent(struct ib_mad_snoop_private *mad_snoop_priv)
+{
+        if (atomic_dec_and_test(&mad_snoop_priv->refcount))
+                complete(&mad_snoop_priv->comp);
+}
+
 static void unregister_mad_agent(struct ib_mad_agent_private *mad_agent_priv)
 {
         struct ib_mad_port_private *port_priv;
@@ -509,9 +521,8 @@ static void unregister_mad_agent(struct ib_mad_agent_private *mad_agent_priv)
         flush_workqueue(port_priv->wq);
         ib_cancel_rmpp_recvs(mad_agent_priv);
 
-        atomic_dec(&mad_agent_priv->refcount);
-        wait_event(mad_agent_priv->wait,
-                   !atomic_read(&mad_agent_priv->refcount));
+        deref_mad_agent(mad_agent_priv);
+        wait_for_completion(&mad_agent_priv->comp);
 
         kfree(mad_agent_priv->reg_req);
         ib_dereg_mr(mad_agent_priv->agent.mr);
@@ -529,9 +540,8 @@ static void unregister_mad_snoop(struct ib_mad_snoop_private *mad_snoop_priv)
         atomic_dec(&qp_info->snoop_count);
         spin_unlock_irqrestore(&qp_info->snoop_lock, flags);
 
-        atomic_dec(&mad_snoop_priv->refcount);
-        wait_event(mad_snoop_priv->wait,
-                   !atomic_read(&mad_snoop_priv->refcount));
+        deref_snoop_agent(mad_snoop_priv);
+        wait_for_completion(&mad_snoop_priv->comp);
 
         kfree(mad_snoop_priv);
 }
@@ -600,8 +610,7 @@ static void snoop_send(struct ib_mad_qp_info *qp_info,
                 spin_unlock_irqrestore(&qp_info->snoop_lock, flags);
                 mad_snoop_priv->agent.snoop_handler(&mad_snoop_priv->agent,
                                                     send_buf, mad_send_wc);
-                if (atomic_dec_and_test(&mad_snoop_priv->refcount))
-                        wake_up(&mad_snoop_priv->wait);
+                deref_snoop_agent(mad_snoop_priv);
                 spin_lock_irqsave(&qp_info->snoop_lock, flags);
         }
         spin_unlock_irqrestore(&qp_info->snoop_lock, flags);
@@ -626,8 +635,7 @@ static void snoop_recv(struct ib_mad_qp_info *qp_info,
                 spin_unlock_irqrestore(&qp_info->snoop_lock, flags);
                 mad_snoop_priv->agent.recv_handler(&mad_snoop_priv->agent,
                                                    mad_recv_wc);
-                if (atomic_dec_and_test(&mad_snoop_priv->refcount))
-                        wake_up(&mad_snoop_priv->wait);
+                deref_snoop_agent(mad_snoop_priv);
                 spin_lock_irqsave(&qp_info->snoop_lock, flags);
         }
         spin_unlock_irqrestore(&qp_info->snoop_lock, flags);
@@ -968,8 +976,7 @@ void ib_free_send_mad(struct ib_mad_send_buf *send_buf)
 
         free_send_rmpp_list(mad_send_wr);
         kfree(send_buf->mad);
-        if (atomic_dec_and_test(&mad_agent_priv->refcount))
-                wake_up(&mad_agent_priv->wait);
+        deref_mad_agent(mad_agent_priv);
 }
 EXPORT_SYMBOL(ib_free_send_mad);
 
@@ -1757,8 +1764,7 @@ static void ib_mad_complete_recv(struct ib_mad_agent_private *mad_agent_priv,
                 mad_recv_wc = ib_process_rmpp_recv_wc(mad_agent_priv,
                                                       mad_recv_wc);
                 if (!mad_recv_wc) {
-                        if (atomic_dec_and_test(&mad_agent_priv->refcount))
-                                wake_up(&mad_agent_priv->wait);
+                        deref_mad_agent(mad_agent_priv);
                         return;
                 }
         }
@@ -1770,8 +1776,7 @@ static void ib_mad_complete_recv(struct ib_mad_agent_private *mad_agent_priv,
                 if (!mad_send_wr) {
                         spin_unlock_irqrestore(&mad_agent_priv->lock, flags);
                         ib_free_recv_mad(mad_recv_wc);
-                        if (atomic_dec_and_test(&mad_agent_priv->refcount))
-                                wake_up(&mad_agent_priv->wait);
+                        deref_mad_agent(mad_agent_priv);
                         return;
                 }
                 ib_mark_mad_done(mad_send_wr);
@@ -1790,8 +1795,7 @@ static void ib_mad_complete_recv(struct ib_mad_agent_private *mad_agent_priv,
         } else {
                 mad_agent_priv->agent.recv_handler(&mad_agent_priv->agent,
                                                    mad_recv_wc);
-                if (atomic_dec_and_test(&mad_agent_priv->refcount))
-                        wake_up(&mad_agent_priv->wait);
+                deref_mad_agent(mad_agent_priv);
         }
 }
 
@@ -2021,8 +2025,7 @@ void ib_mad_complete_send_wr(struct ib_mad_send_wr_private *mad_send_wr,
                                                    mad_send_wc);
 
         /* Release reference on agent taken when sending */
-        if (atomic_dec_and_test(&mad_agent_priv->refcount))
-                wake_up(&mad_agent_priv->wait);
+        deref_mad_agent(mad_agent_priv);
         return;
 done:
         spin_unlock_irqrestore(&mad_agent_priv->lock, flags);