On 28/07/2021 09:19, Yufeng Mo wrote:
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, the range of bond->mode_lock is extended from only bond_3ad_unbind_slave() to both bond_upper_dev_unlink() and bond_3ad_unbind_slave().
[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
drivers/net/bonding/bond_3ad.c | 7 +------ drivers/net/bonding/bond_main.c | 6 +++++- 2 files changed, 6 insertions(+), 7 deletions(-)
[snip]
/** diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c index 0ff7567..deb019e 100644 --- a/drivers/net/bonding/bond_main.c +++ b/drivers/net/bonding/bond_main.c @@ -2129,14 +2129,18 @@ 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
*/ netdev_rx_handler_unregister(slave_dev);
- for this slave anymore.
- /* Sync against bond_3ad_state_machine_handler() */
- spin_lock_bh(&bond->mode_lock);
- bond_upper_dev_unlink(bond, slave);
this calls netdev_upper_dev_unlink() which calls call_netdevice_notifiers_info() for NETDEV_PRECHANGEUPPER and NETDEV_CHANGEUPPER, both of which are allowed to sleep so you cannot hold the mode lock
after netdev_rx_handler_unregister() the bond's recv_probe cannot be executed so you don't really need to unlink it under mode_lock or move mode_lock at all
if (BOND_MODE(bond) == BOND_MODE_8023AD) bond_3ad_unbind_slave(slave);
spin_unlock_bh(&bond->mode_lock);
if (bond_mode_can_use_xmit_hash(bond)) bond_update_slave_arr(bond, slave);