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@xxxxxxxxx>
---
drivers/infiniband/hw/usnic/usnic_ib_verbs.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/drivers/infiniband/hw/usnic/usnic_ib_verbs.c b/drivers/infiniband/hw/usnic/usnic_ib_verbs.c
index 0b91ff3..598e23c 100644
--- 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;
--
2.7.0
