netdev - [PATCH net-next] bonding: fix system hang due to fast igmp timer rescheduling

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Message-Id: <1375205852-31325-1-git-send-email-nikolay@redhat.com>
Date:	Tue, 30 Jul 2013 19:37:32 +0200
From:	Nikolay Aleksandrov <nikolay@...hat.com>
To:	netdev@...r.kernel.org
Cc:	andy@...yhouse.net, fubar@...ibm.com
Subject: [PATCH net-next] bonding: fix system hang due to fast igmp timer rescheduling

From: Nikolay Aleksandrov <Nikolay Aleksandrov nikolay@...hat.com>

After commit 4aa5dee4d9 ("net: convert resend IGMP to notifier event")
we try to acquire rtnl in bond_resend_igmp_join_requests but it can be
scheduled with rtnl already held (e.g. when bond_change_active_slave is
called with rtnl) causing a loop of immediate reschedules + calls because
rtnl_trylock fails each time since it's being already held.
For me this issue leads to system hangs very easy:
modprobe bonding; ifconfig bond0 up; ifenslave bond0 eth0; rmmod
bonding;

The fix is to introduce a small (1 jiffy) delay which is enough for the
sections holding rtnl to finish without putting any strain on the system.

Signed-off-by: Nikolay Aleksandrov <nikolay@...hat.com>
---
 drivers/net/bonding/bond_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index da3af63..9d94313 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -723,7 +723,7 @@ static int bond_set_allmulti(struct bonding *bond, int inc)
 static void bond_resend_igmp_join_requests(struct bonding *bond)
 {
 	if (!rtnl_trylock()) {
-		queue_delayed_work(bond->wq, &bond->mcast_work, 0);
+		queue_delayed_work(bond->wq, &bond->mcast_work, 1);
 		return;
 	}
 	call_netdevice_notifiers(NETDEV_RESEND_IGMP, bond->dev);
-- 
1.8.1.4

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