devlink: Add device lock assert in reload operation

Add an assert to verify that the device lock is always held throughout
reload operations.

Tested the following flows with netdevsim and mlxsw while lockdep is
enabled:

netdevsim:

 # echo "10 1" > /sys/bus/netdevsim/new_device
 # devlink dev reload netdevsim/netdevsim10
 # ip netns add bla
 # devlink dev reload netdevsim/netdevsim10 netns bla
 # ip netns del bla
 # echo 10 > /sys/bus/netdevsim/del_device

mlxsw:

 # devlink dev reload pci/0000:01:00.0
 # ip netns add bla
 # devlink dev reload pci/0000:01:00.0 netns bla
 # ip netns del bla
 # echo 1 > /sys/bus/pci/devices/0000\:01\:00.0/remove
 # echo 1 > /sys/bus/pci/rescan
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/devlink/dev.c

@@ -4,6 +4,7 @@
  * Copyright (c) 2016 Jiri Pirko <jiri@mellanox.com>
  */
 
+#include <linux/device.h>
 #include <net/genetlink.h>
 #include <net/sock.h>
 #include "devl_internal.h"
@@ -433,6 +434,13 @@ int devlink_reload(struct devlink *devlink, struct net *dest_net,
 	struct net *curr_net;
 	int err;
 
+	/* Make sure the reload operations are invoked with the device lock
+	 * held to allow drivers to trigger functionality that expects it
+	 * (e.g., PCI reset) and to close possible races between these
+	 * operations and probe/remove.
+	 */
+	device_lock_assert(devlink->dev);
+
 	memcpy(remote_reload_stats, devlink->stats.remote_reload_stats,
 	       sizeof(remote_reload_stats));