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    Subject[PATCH 4.6 17/81] team: dont call netdev_change_features under team->lock
    Date
    4.6-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Ivan Vecera <ivecera@redhat.com>

    [ 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.

    Fixes: fd867d5 (net/core: generic support for disabling netdev features down stack)
    Cc: Jiri Pirko <jiri@resnulli.us>
    Signed-off-by: Ivan Vecera <ivecera@redhat.com>
    Signed-off-by: Jiri Pirko <jiri@mellanox.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/team/team.c | 9 +++++++--
    1 file changed, 7 insertions(+), 2 deletions(-)

    --- a/drivers/net/team/team.c
    +++ b/drivers/net/team/team.c
    @@ -990,7 +990,7 @@ static void team_port_disable(struct tea
    #define TEAM_ENC_FEATURES (NETIF_F_HW_CSUM | NETIF_F_SG | \
    NETIF_F_RXCSUM | NETIF_F_ALL_TSO)

    -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;
    @@ -1021,15 +1021,20 @@ 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)

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