[PATCH net] team: Fix ABBA deadlock caused by race in team_del_slave

[Jeongjun Park <aha310510@gmail.com>]

       CPU0                    CPU1
       ----                    ----
  lock(&rdev->wiphy.mtx);
                               lock(team->team_lock_key#4);
                               lock(&rdev->wiphy.mtx);
  lock(team->team_lock_key#4);

Deadlock occurs due to the above scenario. Therefore,
modify the code as shown in the patch below to prevent deadlock.

Regards,
Jeongjun Park.

Reported-and-tested-by: syzbot+705c61d60b091ef42c04@syzkaller.appspotmail.com
Fixes: 61dc3461b954 ("team: convert overall spinlock to mutex")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 drivers/net/team/team_core.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/net/team/team_core.c b/drivers/net/team/team_core.c
index ab1935a4aa2c..3ac82df876b0 100644
--- a/drivers/net/team/team_core.c
+++ b/drivers/net/team/team_core.c
@@ -1970,11 +1970,12 @@ static int team_add_slave(struct net_device *dev, struct net_device *port_dev,
                          struct netlink_ext_ack *extack)
 {
        struct team *team = netdev_priv(dev);
-       int err;
+       int err, locked;
 
-       mutex_lock(&team->lock);
+       locked = mutex_trylock(&team->lock);
        err = team_port_add(team, port_dev, extack);
-       mutex_unlock(&team->lock);
+       if (locked)
+               mutex_unlock(&team->lock);
 
        if (!err)
                netdev_change_features(dev);
@@ -1985,11 +1986,12 @@ static int team_add_slave(struct net_device *dev, struct net_device *port_dev,
 static int team_del_slave(struct net_device *dev, struct net_device *port_dev)
 {
        struct team *team = netdev_priv(dev);
-       int err;
+       int err, locked;
 
-       mutex_lock(&team->lock);
+       locked = mutex_trylock(&team->lock);
        err = team_port_del(team, port_dev);
-       mutex_unlock(&team->lock);
+       if (locked)
+               mutex_unlock(&team->lock);
 
        if (err)
                return err;
--