On Thu, 14 Jan 2021 16:34:24 -0800
Saeed Mahameed <sa...@kernel.org> wrote:
> On Thu, 2021-01-14 at 12:55 +0100, Ivan Vecera wrote:
> > Team driver protects port list traversal in team_change_mtu()
> > by its team->lock mutex. This causes a deadlock with certain
> > devices that calls netdev_update_features() during their
> > .ndo_change_mtu() callback. In this case netdev_update_features()
> > calls team's netdevice notifier team_device_event() that in case
> > of NETDEV_FEAT_CHANGE tries lock team->lock mutex again.
> >
> > Example (r8169 case):
> > ...
> > [ 6391.348202] __mutex_lock.isra.6+0x2d0/0x4a0
> > [ 6391.358602] team_device_event+0x9d/0x160 [team]
> > [ 6391.363756] notifier_call_chain+0x47/0x70
> > [ 6391.368329] netdev_update_features+0x56/0x60
> > [ 6391.373207] rtl8169_change_mtu+0x14/0x50 [r8169]
> > [ 6391.378457] dev_set_mtu_ext+0xe1/0x1d0
> > [ 6391.387022] dev_set_mtu+0x52/0x90
> > [ 6391.390820] team_change_mtu+0x64/0xf0 [team]
> > [ 6391.395683] dev_set_mtu_ext+0xe1/0x1d0
> > [ 6391.399963] do_setlink+0x231/0xf50
> > ...
> >
> > To fix the problem the port list traversal in team_change_mtu() can
> > be protected by RCU read lock. In case of failure the failing port
> > is marked and unwind code-path is done also under RCU read lock
> > protection (but not in reverse order).
> >
> > Fixes: 3d249d4ca7d0 ("net: introduce ethernet teaming device")
> > Cc: Jiri Pirko <j...@resnulli.us>
> > Signed-off-by: Ivan Vecera <ivec...@redhat.com>
> > ---
> > drivers/net/team/team.c | 20 ++++++++++----------
> > 1 file changed, 10 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c
> > index c19dac21c468..69d4b28beb17 100644
> > --- a/drivers/net/team/team.c
> > +++ b/drivers/net/team/team.c
> > @@ -1802,35 +1802,35 @@ static int team_set_mac_address(struct
> > net_device *dev, void *p)
> > static int team_change_mtu(struct net_device *dev, int new_mtu)
> > {
> > struct team *team = netdev_priv(dev);
> > - struct team_port *port;
> > + struct team_port *port, *fail_port;
> > int err;
> >
> > - /*
> > - * Alhough this is reader, it's guarded by team lock. It's not
> > possible
> > - * to traverse list in reverse under rcu_read_lock
> > - */
> > - mutex_lock(&team->lock);
> > + rcu_read_lock();
> > team->port_mtu_change_allowed = true;
> > - list_for_each_entry(port, &team->port_list, list) {
> > + list_for_each_entry_rcu(port, &team->port_list, list) {
> > err = dev_set_mtu(port->dev, new_mtu);
>
> some netdevs will need to sleep in their set_mtu, and you can't sleep
> under rcu!
>
> according to your explanation in the commit message the team->lock
> mutex will be also taken under this rcu lock, so this is bad even
> if dev_set_mtu does not sleep.
>
Hmm, you are right... btw do we need to take this mutex at this place?
team_change_mtu() is protected by RTNL, team_device_event() as a netdevice
notifier as well... and team_{add,del}_slave() that modify port list
also.
Thoughts?
Thanks,
Ivan
