netdev - [PATCH net] bonding: fix slave stuck in BOND_LINK

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Message-ID: <15116.1510051807@nyx>
Date:   Tue, 07 Nov 2017 19:50:07 +0900
From:   Jay Vosburgh <jay.vosburgh@...onical.com>
To:     netdev@...r.kernel.org
Cc:     Alex Sidorenko <alexandre.sidorenko@....com>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Jarod Wilson <jarod@...hat.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David Miller" <davem@...emloft.net>
Subject: [PATCH net] bonding: fix slave stuck in BOND_LINK_FAIL state

	The bonding miimon logic has a flaw, in that a failure of the
rtnl_trylock can cause a slave to become permanently stuck in
BOND_LINK_FAIL state.

	The sequence of events to cause this is as follows:

	1) bond_miimon_inspect finds that a slave's link is down, and so
calls bond_propose_link_state, setting slave->new_link_state to
BOND_LINK_FAIL, then sets slave->new_link to BOND_LINK_DOWN and returns
non-zero.

	2) In bond_mii_monitor, the rtnl_trylock fails, and the timer is
rescheduled.  No change is committed.

	3) bond_miimon_inspect is called again, but this time the slave
from step 1 has recovered.  slave->new_link is reset to NOCHANGE, and, as
slave->link was never changed, the switch enters the BOND_LINK_UP case,
and does nothing.  The pending BOND_LINK_FAIL state from step 1 remains
pending, as new_link_state is not reset.

	4) The state from step 3 persists until another slave changes link
state and causes bond_miimon_inspect to return non-zero.  At this point,
the BOND_LINK_FAIL state change on the slave from steps 1-3 is committed,
and the slave will remain stuck in BOND_LINK_FAIL state even though it
is actually link up.

	The remedy for this is to initialize new_link_state on each entry
to bond_miimon_inspect, as is already done with new_link.

Reported-by: Alex Sidorenko <alexandre.sidorenko@....com>
Reviewed-by: Jarod Wilson <jarod@...hat.com>
Signed-off-by: Jay Vosburgh <jay.vosburgh@...onical.com>
Fixes: fb9eb899a6dc ("bonding: handle link transition from FAIL to UP correctly")
---
 drivers/net/bonding/bond_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index c99dc59d729b..167434e952da 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2042,6 +2042,7 @@ static int bond_miimon_inspect(struct bonding *bond)
 
 	bond_for_each_slave_rcu(bond, slave, iter) {
 		slave->new_link = BOND_LINK_NOCHANGE;
+		slave->link_new_state = slave->link;
 
 		link_state = bond_check_dev_link(bond, slave->dev, 0);
 
-- 
2.14.1