Some time ago, I reported a calltrace issue "did not find a suitable aggregator", please see[1]. After a period of analysis and reproduction, I find that this problem is caused by concurrency.

Before the problem occurs, the bond structure is like follows:

bond0 - slaver0(eth0) - agg0.lag_ports -> port0 - port1 \ port0 \ slaver1(eth1) - agg1.lag_ports -> NULL \ port1

If we run 'ifenslave bond0 -d eth1', the process is like below:

excuting __bond_release_one() | bond_upper_dev_unlink()[step1] | | | | | bond_3ad_lacpdu_recv() | | ->bond_3ad_rx_indication() | | spin_lock_bh() | | ->ad_rx_machine() | | ->__record_pdu()[step2] | | spin_unlock_bh() | | | | bond_3ad_state_machine_handler() | spin_lock_bh() | ->ad_port_selection_logic() | ->try to find free aggregator[step3] | ->try to find suitable aggregator[step4] | ->did not find a suitable aggregator[step5] | spin_unlock_bh() | | | | bond_3ad_unbind_slave() | spin_lock_bh() spin_unlock_bh()

step1: already removed slaver1(eth1) from list, but port1 remains step2: receive a lacpdu and update port0 step3: port0 will be removed from agg0.lag_ports. The struct is "agg0.lag_ports -> port1" now, and agg0 is not free. At the same time, slaver1/agg1 has been removed from the list by step1. So we can't find a free aggregator now. step4: can't find suitable aggregator because of step2 step5: cause a calltrace since port->aggregator is NULL

To solve this concurrency problem, put bond_upper_dev_unlink() after bond_3ad_unbind_slave(). In this way, we can invalid the port first and skip this port in bond_3ad_state_machine_handler(). This eliminates the situation that the slaver has been removed from the list but the port is still valid.

[1]https://lore.kernel.org/netdev/10374.1611947473@famine/

Signed-off-by: Yufeng Mo moyufeng@huawei.com Acked-by: Jay Vosburgh jay.vosburgh@canonical.com --- ChangeLogs: V1 -> V2: Modify the method of resolving concurrency because bond_upper_dev_unlink() may sleep and cannot hold mode lock. --- drivers/net/bonding/bond_main.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c index d22d783..c23f39e 100644 --- a/drivers/net/bonding/bond_main.c +++ b/drivers/net/bonding/bond_main.c @@ -2252,7 +2252,6 @@ static int __bond_release_one(struct net_device *bond_dev, /* recompute stats just before removing the slave */ bond_get_stats(bond->dev, &bond->bond_stats);

- bond_upper_dev_unlink(bond, slave); /* unregister rx_handler early so bond_handle_frame wouldn't be called * for this slave anymore. */ @@ -2261,6 +2260,8 @@ static int __bond_release_one(struct net_device *bond_dev, if (BOND_MODE(bond) == BOND_MODE_8023AD) bond_3ad_unbind_slave(slave);

+ bond_upper_dev_unlink(bond, slave); + if (bond_mode_can_use_xmit_hash(bond)) bond_update_slave_arr(bond, slave);