Commit 9d3e1c09 authored Dec 11, 2018 by Parvi Kaustubhi Committed by Greg Kroah-Hartman Jan 26, 2019

IB/usnic: Fix potential deadlock



[ 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@cisco.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent d9c25a6f

drivers/infiniband/hw/usnic/usnic_ib_verbs.c

+7 −4

Original line number	Diff line number	Diff line
		@@ -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;