Re: [PATCH net-next] bonding: 3ad: fix the concurrency between __bond_release_one() and bond_3ad_state_machine_handler()

On 28/07/2021 10:34, Nikolay Aleksandrov wrote:

On 28/07/2021 09:19, Yufeng Mo wrote:

quoted

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/ (local)

Signed-off-by: Yufeng Mo <redacted>
Acked-by: Jay Vosburgh <redacted>
---
 drivers/net/bonding/bond_3ad.c  | 7 +------
 drivers/net/bonding/bond_main.c | 6 +++++-
 2 files changed, 6 insertions(+), 7 deletions(-)

[snip]
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

^^^^
Forget this part of the comment, I saw later that you don't want to receive
lacpdu on the other port

The notifier sleep problem still exists though.

quoted

 	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);