[IB] umad: avoid potential deadlock when unregistering MAD agents

ib_unregister_mad_agent() completes all pending MAD sends and waits
for the agent's send_handler routine to return.  umad's send_handler()
calls queue_packet(), which does down_read() on the port mutex to look
up the agent ID.  This means that the port mutex cannot be held for
writing while calling ib_unregister_mad_agent(), or else it will
deadlock.  This patch fixes all the calls to ib_unregister_mad_agent()
in the umad module to avoid this deadlock.

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

1 files changed, 17 insertions, 12 deletions

diff --git a/drivers/infiniband/core/user_mad.c b/drivers/infiniband/core/user_mad.c
index 6aefeed42ab..f5ed36c2a06 100644
--- a/drivers/infiniband/core/user_mad.c
+++ b/drivers/infiniband/core/user_mad.c
@@ -505,8 +505,6 @@ found:
                 goto out;
         }
 
-        file->agent[agent_id] = agent;
-
         file->mr[agent_id] = ib_get_dma_mr(agent->qp->pd, IB_ACCESS_LOCAL_WRITE);
         if (IS_ERR(file->mr[agent_id])) {
                 ret = -ENOMEM;
@@ -519,14 +517,15 @@ found:
                 goto err_mr;
         }
 
+        file->agent[agent_id] = agent;
         ret = 0;
+
         goto out;
 
 err_mr:
         ib_dereg_mr(file->mr[agent_id]);
 
 err:
-        file->agent[agent_id] = NULL;
         ib_unregister_mad_agent(agent);
 
 out:
@@ -536,27 +535,33 @@ out:
 
 static int ib_umad_unreg_agent(struct ib_umad_file *file, unsigned long arg)
 {
+        struct ib_mad_agent *agent = NULL;
+        struct ib_mr *mr = NULL;
         u32 id;
         int ret = 0;
 
-        down_write(&file->port->mutex);
+        if (get_user(id, (u32 __user *) arg))
+                return -EFAULT;
 
-        if (get_user(id, (u32 __user *) arg)) {
-                ret = -EFAULT;
-                goto out;
-        }
+        down_write(&file->port->mutex);
 
         if (id < 0 || id >= IB_UMAD_MAX_AGENTS || !file->agent[id]) {
                 ret = -EINVAL;
                 goto out;
         }
 
-        ib_dereg_mr(file->mr[id]);
-        ib_unregister_mad_agent(file->agent[id]);
+        agent = file->agent[id];
+        mr    = file->mr[id];
         file->agent[id] = NULL;
 
 out:
         up_write(&file->port->mutex);
+
+        if (agent) {
+                ib_unregister_mad_agent(agent);
+                ib_dereg_mr(mr);
+        }
+
         return ret;
 }
 
@@ -623,16 +628,16 @@ static int ib_umad_close(struct inode *inode, struct file *filp)
         struct ib_umad_packet *packet, *tmp;
         int i;
 
-        down_write(&file->port->mutex);
         for (i = 0; i < IB_UMAD_MAX_AGENTS; ++i)
                 if (file->agent[i]) {
-                        ib_dereg_mr(file->mr[i]);
                         ib_unregister_mad_agent(file->agent[i]);
+                        ib_dereg_mr(file->mr[i]);
                 }
 
         list_for_each_entry_safe(packet, tmp, &file->recv_list, list)
                 kfree(packet);
 
+        down_write(&file->port->mutex);
         list_del(&file->port_list);
         up_write(&file->port->mutex);