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    Subject[PATCH AUTOSEL 5.14 097/252] bonding: 3ad: fix the concurrency between __bond_release_one() and bond_3ad_state_machine_handler()
    Date
    From: Yufeng Mo <moyufeng@huawei.com>

    [ Upstream commit 220ade77452c15ecb1ab94c3f8aaeb6d033c3582 ]

    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>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 31730efa7538..8aef6005bfee 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);

    --
    2.30.2

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