[PATCH net] bonding: switch bond_miimon_inspect to rtnl lock

[Stanislav Fomichev <stfomichev@gmail.com>]

Syzkaller reports the following issue:

 RTNL: assertion failed at ./include/net/netdev_lock.h (72)
 WARNING: CPU: 0 PID: 1141 at ./include/net/netdev_lock.h:72 netdev_ops_assert_locked include/net/netdev_lock.h:72 [inline]
 WARNING: CPU: 0 PID: 1141 at ./include/net/netdev_lock.h:72 __linkwatch_sync_dev+0x1ed/0x230 net/core/link_watch.c:279

 ethtool_op_get_link+0x1d/0x70 net/ethtool/ioctl.c:63
 bond_check_dev_link+0x3f9/0x710 drivers/net/bonding/bond_main.c:863
 bond_miimon_inspect drivers/net/bonding/bond_main.c:2745 [inline]
 bond_mii_monitor+0x3c0/0x2dc0 drivers/net/bonding/bond_main.c:2967
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
 kthread+0x3c5/0x780 kernel/kthread.c:464
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

As discussed in [0], the report is a bit bogus, but it exposes
the fact that bond_miimon_inspect might sleep while its being
called under RCU read lock. Convert bond_miimon_inspect callers
(bond_mii_monitor) to rtnl lock.

Reported-by: syzbot+b8c48ea38ca27d150063@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b8c48ea38ca27d150063
Link: http://lore.kernel.org/netdev/aEt6LvBMwUMxmUyx@mini-arch [0]
Fixes: f7a11cba0ed7 ("bonding: hold ops lock around get_link")
Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
---
 drivers/net/bonding/bond_main.c | 34 +++++++++++++--------------------
 1 file changed, 13 insertions(+), 21 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index c4d53e8e7c15..ab40f0828680 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2720,7 +2720,6 @@ static int bond_slave_info_query(struct net_device *bond_dev, struct ifslave *in
 
 /*-------------------------------- Monitoring -------------------------------*/
 
-/* called with rcu_read_lock() */
 static int bond_miimon_inspect(struct bonding *bond)
 {
 	bool ignore_updelay = false;
@@ -2729,17 +2728,17 @@ static int bond_miimon_inspect(struct bonding *bond)
 	struct slave *slave;
 
 	if (BOND_MODE(bond) == BOND_MODE_ACTIVEBACKUP) {
-		ignore_updelay = !rcu_dereference(bond->curr_active_slave);
+		ignore_updelay = !rtnl_dereference(bond->curr_active_slave);
 	} else {
 		struct bond_up_slave *usable_slaves;
 
-		usable_slaves = rcu_dereference(bond->usable_slaves);
+		usable_slaves = rtnl_dereference(bond->usable_slaves);
 
 		if (usable_slaves && usable_slaves->count == 0)
 			ignore_updelay = true;
 	}
 
-	bond_for_each_slave_rcu(bond, slave, iter) {
+	bond_for_each_slave(bond, slave, iter) {
 		bond_propose_link_state(slave, BOND_LINK_NOCHANGE);
 
 		link_state = bond_check_dev_link(bond, slave->dev, 0);
@@ -2962,35 +2961,28 @@ static void bond_mii_monitor(struct work_struct *work)
 	if (!bond_has_slaves(bond))
 		goto re_arm;
 
-	rcu_read_lock();
+	/* Race avoidance with bond_close cancel of workqueue */
+	if (!rtnl_trylock()) {
+		delay = 1;
+		should_notify_peers = false;
+		goto re_arm;
+	}
+
 	should_notify_peers = bond_should_notify_peers(bond);
 	commit = !!bond_miimon_inspect(bond);
 	if (bond->send_peer_notif) {
-		rcu_read_unlock();
-		if (rtnl_trylock()) {
-			bond->send_peer_notif--;
-			rtnl_unlock();
-		}
-	} else {
-		rcu_read_unlock();
+		bond->send_peer_notif--;
 	}
 
 	if (commit) {
-		/* Race avoidance with bond_close cancel of workqueue */
-		if (!rtnl_trylock()) {
-			delay = 1;
-			should_notify_peers = false;
-			goto re_arm;
-		}
-
 		bond_for_each_slave(bond, slave, iter) {
 			bond_commit_link_state(slave, BOND_SLAVE_NOTIFY_LATER);
 		}
 		bond_miimon_commit(bond);
-
-		rtnl_unlock();	/* might sleep, hold no other locks */
 	}
 
+	rtnl_unlock();	/* might sleep, hold no other locks */
+
 re_arm:
 	if (bond->params.miimon)
 		queue_delayed_work(bond->wq, &bond->mii_work, delay);
-- 
2.49.0