netdev - [PATCH net-next] bonding: 3ad: fix the concurrency between __bond_release_one() and bond_3ad_state_machine

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Date:   Wed, 28 Jul 2021 14:19:52 +0800
From:   Yufeng Mo <moyufeng@...wei.com>
To:     <davem@...emloft.net>, <kuba@...nel.org>,
        <jay.vosburgh@...onical.com>, <jiri@...nulli.us>
CC:     <netdev@...r.kernel.org>, <shenjian15@...wei.com>,
        <lipeng321@...wei.com>, <yisen.zhuang@...wei.com>,
        <linyunsheng@...wei.com>, <zhangjiaran@...wei.com>,
        <huangguangbin2@...wei.com>, <chenhao288@...ilicon.com>,
        <salil.mehta@...wei.com>, <moyufeng@...wei.com>,
        <linuxarm@...wei.com>, <linuxarm@...neuler.org>
Subject: [PATCH net-next] bonding: 3ad: fix the concurrency between __bond_release_one() and bond_3ad_state_machine_handler()

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@...wei.com>
Acked-by: Jay Vosburgh <jay.vosburgh@...onical.com>
---
 drivers/net/bonding/bond_3ad.c  | 7 +------
 drivers/net/bonding/bond_main.c | 6 +++++-
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
index 6908822..f0f5adb 100644
--- a/drivers/net/bonding/bond_3ad.c
+++ b/drivers/net/bonding/bond_3ad.c
@@ -2099,15 +2099,13 @@ void bond_3ad_unbind_slave(struct slave *slave)
 	struct list_head *iter;
 	bool dummy_slave_update; /* Ignore this value as caller updates array */
 
-	/* Sync against bond_3ad_state_machine_handler() */
-	spin_lock_bh(&bond->mode_lock);
 	aggregator = &(SLAVE_AD_INFO(slave)->aggregator);
 	port = &(SLAVE_AD_INFO(slave)->port);
 
 	/* if slave is null, the whole port is not initialized */
 	if (!port->slave) {
 		slave_warn(bond->dev, slave->dev, "Trying to unbind an uninitialized port\n");
-		goto out;
+		return;
 	}
 
 	slave_dbg(bond->dev, slave->dev, "Unbinding Link Aggregation Group %d\n",
@@ -2239,9 +2237,6 @@ void bond_3ad_unbind_slave(struct slave *slave)
 		}
 	}
 	port->slave = NULL;
-
-out:
-	spin_unlock_bh(&bond->mode_lock);
 }
 
 /**
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
 	 * for this slave anymore.
 	 */
 	netdev_rx_handler_unregister(slave_dev);
 
+	/* Sync against bond_3ad_state_machine_handler() */
+	spin_lock_bh(&bond->mode_lock);
+	bond_upper_dev_unlink(bond, slave);
+
 	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);
-- 
2.8.1