IB/usnic: Fix potential deadlock

Acquiring the rtnl lock while holding usdev_lock could result in a
deadlock.

For example:

usnic_ib_query_port()
| mutex_lock(&us_ibdev->usdev_lock)
 | ib_get_eth_speed()
  | rtnl_lock()

rtnl_lock()
| usnic_ib_netdevice_event()
 | mutex_lock(&us_ibdev->usdev_lock)

This commit moves the usdev_lock acquisition after the rtnl lock has been
released.

This is safe to do because usdev_lock is not protecting anything being
accessed in ib_get_eth_speed(). Hence, the correct order of holding locks
(rtnl -> usdev_lock) is not violated.

Signed-off-by: Parvi Kaustubhi <pkaustub@cisco.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/drivers/infiniband/hw/usnic/usnic_ib_verbs.c b/drivers/infiniband/hw/usnic/usnic_ib_verbs.c
index 1b9f69d..1d4abef 100644 (file)
--- a/drivers/infiniband/hw/usnic/usnic_ib_verbs.c
+++ b/drivers/infiniband/hw/usnic/usnic_ib_verbs.c
@@ -336,13 +336,16 @@ int usnic_ib_query_port(struct ib_device *ibdev, u8 port,
 
        usnic_dbg("\n");
 
-       mutex_lock(&us_ibdev->usdev_lock);
        if (ib_get_eth_speed(ibdev, port, &props->active_speed,
-                            &props->active_width)) {
-               mutex_unlock(&us_ibdev->usdev_lock);
+                            &props->active_width))
                return -EINVAL;
-       }
 
+       /*
+        * usdev_lock is acquired after (and not before) ib_get_eth_speed call
+        * because acquiring rtnl_lock in ib_get_eth_speed, while holding
+        * usdev_lock could lead to a deadlock.
+        */
+       mutex_lock(&us_ibdev->usdev_lock);
        /* props being zeroed by the caller, avoid zeroing it here */
 
        props->lid = 0;