Patch "team: don't call netdev_change_features under team->lock" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

    team: don't call netdev_change_features under team->lock

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
team-don-t-call-netdev_change_features-under-team-lock.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ivan Vecera <[email protected]>
Date: Wed, 25 May 2016 21:21:52 +0200
Subject: team: don't call netdev_change_features under team->lock

From: Ivan Vecera <[email protected]>

[ Upstream commit f6988cb63a4e698d8a62a1d085d263d1fcc351ea ]

The team_device_event() notifier calls team_compute_features() to fix vlan_features under team->lock to protect team->port_list. The problem is that subsequent __team_compute_features() calls netdev_change_features() to propagate vlan_features to upper vlan devices while team->lock is still taken. This can lead to deadlock when NETIF_F_LRO is modified on lower devices or team device itself.

Example:
The team0 as active backup with eth0 and eth1 NICs. Both eth0 & eth1 are LRO capable and LRO is enabled. Thus LRO is also enabled on team0.

The command 'ethtool -K team0 lro off' now hangs due to this deadlock:

dev_ethtool()
-> ethtool_set_features()
-> __netdev_update_features(team)
-> netdev_sync_lower_features()
-> netdev_update_features(lower_1)

    -> __netdev_update_features(lower_1)
    -> netdev_features_change(lower_1)
     -> call_netdevice_notifiers(...)
      -> team_device_event(lower_1)
       -> team_compute_features(team) [TAKES team->lock]
        -> netdev_change_features(team)
         -> __netdev_update_features(team)
          -> netdev_sync_lower_features()
           -> netdev_update_features(lower_2)
            -> __netdev_update_features(lower_2)
            -> netdev_features_change(lower_2)
             -> call_netdevice_notifiers(...)
              -> team_device_event(lower_2)
               -> team_compute_features(team) [DEADLOCK]

The bug is present in team from the beginning but it appeared after the commit fd867d5 (net/core: generic support for disabling netdev features down stack) that adds synchronization of features with lower devices.

---
 drivers/net/team/team.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

@@ -969,7 +969,7 @@ static void team_port_disable(struct tea
 			    NETIF_F_FRAGLIST | NETIF_F_ALL_TSO | \
 			    NETIF_F_HIGHDMA | NETIF_F_LRO)
 
-static void __team_compute_features(struct team *team)
+static void ___team_compute_features(struct team *team)
 {
 	struct team_port *port;
 	u32 vlan_features = TEAM_VLAN_FEATURES & NETIF_F_ALL_FOR_ALL;

@@ -993,15 +993,20 @@ static void __team_compute_features(stru
 	team->dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
 	if (dst_release_flag == (IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM))
 		team->dev->priv_flags |= IFF_XMIT_DST_RELEASE;
+}
 
+static void __team_compute_features(struct team *team)
+{
+	___team_compute_features(team);
 	netdev_change_features(team->dev);
 }
 
 static void team_compute_features(struct team *team)
 {
 	mutex_lock(&team->lock);
-	__team_compute_features(team);
+	___team_compute_features(team);
 	mutex_unlock(&team->lock);
+	netdev_change_features(team->dev);
 }
 
 static int team_port_enter(struct team *team, struct team_port *port)

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/team-don-t-call-netdev_change_features-under-team-lock.patch