From: Vladimir Oltean vladimir.oltean@nxp.com
[ Upstream commit 6ca3c005d0604e8d2b439366e3923ea58db99641 ]
According to the synchronization rules for .ndo_get_stats() as seen in Documentation/networking/netdevices.rst, acquiring a plain spin_lock() should not be illegal, but the bridge driver implementation makes it so.
After running these commands, I am being faced with the following lockdep splat:
$ ip link add link swp0 name macsec0 type macsec encrypt on && ip link set swp0 up $ ip link add dev br0 type bridge vlan_filtering 1 && ip link set br0 up $ ip link set macsec0 master br0 && ip link set macsec0 up
======================================================== WARNING: possible irq lock inversion dependency detected 6.4.0-04295-g31b577b4bd4a #603 Not tainted -------------------------------------------------------- swapper/1/0 just changed the state of lock: ffff6bd348724cd8 (&br->lock){+.-.}-{3:3}, at: br_forward_delay_timer_expired+0x34/0x198 but this lock took another, SOFTIRQ-unsafe lock in the past: (&ocelot->stats_lock){+.+.}-{3:3}
and interrupts could create inverse lock ordering between them.
other info that might help us debug this: Chain exists of: &br->lock --> &br->hash_lock --> &ocelot->stats_lock
Possible interrupt unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&ocelot->stats_lock); local_irq_disable(); lock(&br->lock); lock(&br->hash_lock); <Interrupt> lock(&br->lock);
*** DEADLOCK ***
(details about the 3 locks skipped)
swp0 is instantiated by drivers/net/dsa/ocelot/felix.c, and this only matters to the extent that its .ndo_get_stats64() method calls spin_lock(&ocelot->stats_lock).
Documentation/locking/lockdep-design.rst says:
| A lock is irq-safe means it was ever used in an irq context, while a lock | is irq-unsafe means it was ever acquired with irq enabled.
(...)
| Furthermore, the following usage based lock dependencies are not allowed | between any two lock-classes:: | | <hardirq-safe> -> <hardirq-unsafe> | <softirq-safe> -> <softirq-unsafe>
Lockdep marks br->hash_lock as softirq-safe, because it is sometimes taken in softirq context (for example br_fdb_update() which runs in NET_RX softirq), and when it's not in softirq context it blocks softirqs by using spin_lock_bh().
Lockdep marks ocelot->stats_lock as softirq-unsafe, because it never blocks softirqs from running, and it is never taken from softirq context. So it can always be interrupted by softirqs.
There is a call path through which a function that holds br->hash_lock: fdb_add_hw_addr() will call a function that acquires ocelot->stats_lock: ocelot_port_get_stats64(). This can be seen below:
ocelot_port_get_stats64+0x3c/0x1e0 felix_get_stats64+0x20/0x38 dsa_slave_get_stats64+0x3c/0x60 dev_get_stats+0x74/0x2c8 rtnl_fill_stats+0x4c/0x150 rtnl_fill_ifinfo+0x5cc/0x7b8 rtmsg_ifinfo_build_skb+0xe4/0x150 rtmsg_ifinfo+0x5c/0xb0 __dev_notify_flags+0x58/0x200 __dev_set_promiscuity+0xa0/0x1f8 dev_set_promiscuity+0x30/0x70 macsec_dev_change_rx_flags+0x68/0x88 __dev_set_promiscuity+0x1a8/0x1f8 __dev_set_rx_mode+0x74/0xa8 dev_uc_add+0x74/0xa0 fdb_add_hw_addr+0x68/0xd8 fdb_add_local+0xc4/0x110 br_fdb_add_local+0x54/0x88 br_add_if+0x338/0x4a0 br_add_slave+0x20/0x38 do_setlink+0x3a4/0xcb8 rtnl_newlink+0x758/0x9d0 rtnetlink_rcv_msg+0x2f0/0x550 netlink_rcv_skb+0x128/0x148 rtnetlink_rcv+0x24/0x38
the plain English explanation for it is:
The macsec0 bridge port is created without p->flags & BR_PROMISC, because it is what br_manage_promisc() decides for a VLAN filtering bridge with a single auto port.
As part of the br_add_if() procedure, br_fdb_add_local() is called for the MAC address of the device, and this results in a call to dev_uc_add() for macsec0 while the softirq-safe br->hash_lock is taken.
Because macsec0 does not have IFF_UNICAST_FLT, dev_uc_add() ends up calling __dev_set_promiscuity() for macsec0, which is propagated by its implementation, macsec_dev_change_rx_flags(), to the lower device: swp0. This triggers the call path:
dev_set_promiscuity(swp0) -> rtmsg_ifinfo() -> dev_get_stats() -> ocelot_port_get_stats64()
with a calling context that lockdep doesn't like (br->hash_lock held).
Normally we don't see this, because even though many drivers that can be bridge ports don't support IFF_UNICAST_FLT, we need a driver that
(a) doesn't support IFF_UNICAST_FLT, *and* (b) it forwards the IFF_PROMISC flag to another driver, and (c) *that* driver implements ndo_get_stats64() using a softirq-unsafe spinlock.
Condition (b) is necessary because the first __dev_set_rx_mode() calls __dev_set_promiscuity() with "bool notify=false", and thus, the rtmsg_ifinfo() code path won't be entered.
The same criteria also hold true for DSA switches which don't report IFF_UNICAST_FLT. When the DSA master uses a spin_lock() in its ndo_get_stats64() method, the same lockdep splat can be seen.
I think the deadlock possibility is real, even though I didn't reproduce it, and I'm thinking of the following situation to support that claim:
fdb_add_hw_addr() runs on a CPU A, in a context with softirqs locally disabled and br->hash_lock held, and may end up attempting to acquire ocelot->stats_lock.
In parallel, ocelot->stats_lock is currently held by a thread B (say, ocelot_check_stats_work()), which is interrupted while holding it by a softirq which attempts to lock br->hash_lock.
Thread B cannot make progress because br->hash_lock is held by A. Whereas thread A cannot make progress because ocelot->stats_lock is held by B.
When taking the issue at face value, the bridge can avoid that problem by simply making the ports promiscuous from a code path with a saner calling context (br->hash_lock not held). A bridge port without IFF_UNICAST_FLT is going to become promiscuous as soon as we call dev_uc_add() on it (which we do unconditionally), so why not be preemptive and make it promiscuous right from the beginning, so as to not be taken by surprise.
With this, we've broken the links between code that holds br->hash_lock or br->lock and code that calls into the ndo_change_rx_flags() or ndo_get_stats64() ops of the bridge port.
Fixes: 2796d0c648c9 ("bridge: Automatically manage port promiscuous mode.") Signed-off-by: Vladimir Oltean vladimir.oltean@nxp.com Reviewed-by: Ido Schimmel idosch@nvidia.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/bridge/br_if.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c index 3f04b40f60568..2450690f98cfa 100644 --- a/net/bridge/br_if.c +++ b/net/bridge/br_if.c @@ -166,8 +166,9 @@ void br_manage_promisc(struct net_bridge *br) * This lets us disable promiscuous mode and write * this config to hw. */ - if (br->auto_cnt == 0 || - (br->auto_cnt == 1 && br_auto_port(p))) + if ((p->dev->priv_flags & IFF_UNICAST_FLT) && + (br->auto_cnt == 0 || + (br->auto_cnt == 1 && br_auto_port(p)))) br_port_clear_promisc(p); else br_port_set_promisc(p);