[PATCH 4.14 50/63] IB/usnic: Fix potential deadlock

From: Greg Kroah-Hartman
Date: Thu Jan 24 2019 - 14:33:02 EST


4.14-stable review patch. If anyone has any objections, please let me know.

------------------

[ Upstream commit 8036e90f92aae2784b855a0007ae2d8154d28b3c ]

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>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 3c3453d213dc..fdfa25059723 100644
--- a/drivers/infiniband/hw/usnic/usnic_ib_verbs.c
+++ b/drivers/infiniband/hw/usnic/usnic_ib_verbs.c
@@ -310,13 +310,16 @@ 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;
--
2.19.1