IB/mad: Fix oopsable race on device removal

Fix an oopsable race debugged by Eli Cohen <eli@mellanox.co.il>:
After removing the port from port_list, ib_mad_port_close flushes
port_priv->wq before destroying the special QPs. This means that a
completion event could arrive, and queue a new work in this work queue
after flush.

This patch also removes an unnecessary flush_workqueue():
destroy_workqueue() already includes a flush.

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

1 files changed, 14 insertions, 7 deletions

diff --git a/drivers/infiniband/core/mad.c b/drivers/infiniband/core/mad.c
index 16549add8e8f..f7854b65fd55 100644
--- a/drivers/infiniband/core/mad.c
+++ b/drivers/infiniband/core/mad.c
@@ -2364,8 +2364,12 @@ static void timeout_sends(void *data)
 static void ib_mad_thread_completion_handler(struct ib_cq *cq, void *arg)
 {
         struct ib_mad_port_private *port_priv = cq->cq_context;
+        unsigned long flags;
 
-        queue_work(port_priv->wq, &port_priv->work);
+        spin_lock_irqsave(&ib_mad_port_list_lock, flags);
+        if (!list_empty(&port_priv->port_list))
+                queue_work(port_priv->wq, &port_priv->work);
+        spin_unlock_irqrestore(&ib_mad_port_list_lock, flags);
 }
 
 /*
@@ -2677,18 +2681,23 @@ static int ib_mad_port_open(struct ib_device *device,
         }
         INIT_WORK(&port_priv->work, ib_mad_completion_handler, port_priv);
 
+        spin_lock_irqsave(&ib_mad_port_list_lock, flags);
+        list_add_tail(&port_priv->port_list, &ib_mad_port_list);
+        spin_unlock_irqrestore(&ib_mad_port_list_lock, flags);
+
         ret = ib_mad_port_start(port_priv);
         if (ret) {
                 printk(KERN_ERR PFX "Couldn't start port\n");
                 goto error9;
         }
 
-        spin_lock_irqsave(&ib_mad_port_list_lock, flags);
-        list_add_tail(&port_priv->port_list, &ib_mad_port_list);
-        spin_unlock_irqrestore(&ib_mad_port_list_lock, flags);
         return 0;
 
 error9:
+        spin_lock_irqsave(&ib_mad_port_list_lock, flags);
+        list_del_init(&port_priv->port_list);
+        spin_unlock_irqrestore(&ib_mad_port_list_lock, flags);
+
         destroy_workqueue(port_priv->wq);
 error8:
         destroy_mad_qp(&port_priv->qp_info[1]);
@@ -2725,11 +2734,9 @@ static int ib_mad_port_close(struct ib_device *device, int port_num)
                 printk(KERN_ERR PFX "Port %d not found\n", port_num);
                 return -ENODEV;
         }
-        list_del(&port_priv->port_list);
+        list_del_init(&port_priv->port_list);
         spin_unlock_irqrestore(&ib_mad_port_list_lock, flags);
 
-        /* Stop processing completions. */
-        flush_workqueue(port_priv->wq);
         destroy_workqueue(port_priv->wq);
         destroy_mad_qp(&port_priv->qp_info[1]);
         destroy_mad_qp(&port_priv->qp_info[0]);