Subject: Re: [RFC] bonding: fix workqueue re-arming races

From: Jay Vosburgh <[email-masked]>
Date: Tue, 31 Aug 2010 13:54:23 -0700

Jiri Bohac <[email-masked]> wrote:

>Hi,
>
>this is another attempt to solve the bonding workqueue re-arming
>races.
>
>The issue has been thoroughly discussed here:
>http://article.gmane.org/gmane.linux.network/146949 "[PATCH]
>bonding: cancel_delayed_work() -> cancel_delayed_work_sync()"
>However, the only outcome was a proposal for an ugly hack with
>busy-waiting on the rtnl.
>
>The problem:
>Bonding uses delayed work that automatically re-arms itself,
>e.g.: bond_mii_monitor().
>
>A dev->close() quickly followed by dev->open() on the bonding
>master has a race condition. bond_close() sets kill_timers=1 and
>calls cancel_delayed_work(), hoping that bond_mii_monitor() will
>not re-arm again anymore.  There are two problems with this:
>
>- bond->kill_timers is not re-checked after re-acquiring the
>  bond->lock (this would be easy to fix)
>
>- bond_open() resets bond->kill_timers to 0. If this happens
>  before bond_mii_monitor() notices the flag and exits, it will
>  re-arm itself. bond_open() then tries to schedule the delayed
>  work, which causes a BUG.
>
>The issue would be solved by calling cancel_delayed_work_sync(),
>but this can not be done from bond_close() since it is called
>under rtnl and the delayed work locks rtnl itself.
>
>My proposal is to move all the "commit" work that requires rtnl
>to a separate work and schedule it on the bonding wq. Thus, the
>re-arming work does not need rtnl and can be cancelled using
>cancel_delayed_work_sync().
>
>Comments?
>
>[note, this does not deal with bond_loadbalance_arp_mon(), where
>rtnl is now taken as well in net-next; I'll do this if you think
>the idea is good ]

	I don't believe the loadbalance_arp_mon acquires RTNL in
net-next.  I recall discussing this with Andy not too long ago, but I
didn't think that change went in, and I don't see it in the tree.

>Signed-off-by: Jiri Bohac <[email-masked]>
>
>diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
>index 822f586..8015e12 100644
>--- a/drivers/net/bonding/bond_3ad.c
>+++ b/drivers/net/bonding/bond_3ad.c
>@@ -2119,10 +2119,6 @@ void bond_3ad_state_machine_handler(struct work_struct *work)
>
> 	read_lock(&bond->lock);
>
>-	if (bond->kill_timers) {
>-		goto out;
>-	}
>-
> 	//check if there are any slaves
> 	if (bond->slave_cnt == 0) {
> 		goto re_arm;
>@@ -2166,7 +2162,6 @@ void bond_3ad_state_machine_handler(struct work_struct *work)
>
> re_arm:
> 	queue_delayed_work(bond->wq, &bond->ad_work, ad_delta_in_ticks);
>-out:
> 	read_unlock(&bond->lock);
> }
>
>diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
>index c746b33..250d027 100644
>--- a/drivers/net/bonding/bond_alb.c
>+++ b/drivers/net/bonding/bond_alb.c
>@@ -1397,6 +1397,23 @@ out:
> 	return NETDEV_TX_OK;
> }
>
>+void bond_alb_promisc_disable(struct work_struct *work)
>+{
>+	struct bonding *bond = container_of(work, struct bonding,
>+					    alb_promisc_disable_work);
>+	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
>+
>+	/*
>+	 * dev_set_promiscuity requires rtnl and
>+	 * nothing else.
>+	 */
>+	rtnl_lock();
>+	dev_set_promiscuity(bond->curr_active_slave->dev, -1);
>+	bond_info->primary_is_promisc = 0;
>+	bond_info->rlb_promisc_timeout_counter = 0;
>+	rtnl_unlock();
>+}

	What prevents this from deadlocking such that cpu A is in
bond_close, holding RTNL and in cancel_delayed_work_sync, while cpu B is
in the above function, trying to acquire RTNL?

	Also, assuming for the moment that the above isn't a problem,
curr_active_slave may be NULL if the last slave is removed between the
time bond_alb_promisc_disable is scheduled and when it runs.  I'm not
sure that the alb_bond_info can be guaranteed to be valid, either, if
the mode changed.

	-J

> void bond_alb_monitor(struct work_struct *work)
> {
> 	struct bonding *bond = container_of(work, struct bonding,
>@@ -1407,10 +1424,6 @@ void bond_alb_monitor(struct work_struct *work)
>
> 	read_lock(&bond->lock);
>
>-	if (bond->kill_timers) {
>-		goto out;
>-	}
>-
> 	if (bond->slave_cnt == 0) {
> 		bond_info->tx_rebalance_counter = 0;
> 		bond_info->lp_counter = 0;
>@@ -1462,25 +1475,11 @@ void bond_alb_monitor(struct work_struct *work)
> 	if (bond_info->rlb_enabled) {
> 		if (bond_info->primary_is_promisc &&
> 		    (++bond_info->rlb_promisc_timeout_counter >= RLB_PROMISC_TIMEOUT)) {
>-
>-			/*
>-			 * dev_set_promiscuity requires rtnl and
>-			 * nothing else.
>-			 */
>-			read_unlock(&bond->lock);
>-			rtnl_lock();
>-
>-			bond_info->rlb_promisc_timeout_counter = 0;
>-
> 			/* If the primary was set to promiscuous mode
> 			 * because a slave was disabled then
> 			 * it can now leave promiscuous mode.
> 			 */
>-			dev_set_promiscuity(bond->curr_active_slave->dev, -1);
>-			bond_info->primary_is_promisc = 0;
>-
>-			rtnl_unlock();
>-			read_lock(&bond->lock);
>+			queue_work(bond->wq, &bond->alb_promisc_disable_work);
> 		}
>
> 		if (bond_info->rlb_rebalance) {
>@@ -1505,7 +1504,6 @@ void bond_alb_monitor(struct work_struct *work)
>
> re_arm:
> 	queue_delayed_work(bond->wq, &bond->alb_work, alb_delta_in_ticks);
>-out:
> 	read_unlock(&bond->lock);
> }
>
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index 2cc4cfc..3e8b57e 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -2343,10 +2343,15 @@ static int bond_miimon_inspect(struct bonding *bond)
> 	return commit;
> }
>
>-static void bond_miimon_commit(struct bonding *bond)
>+static void bond_miimon_commit(struct work_struct *work)
> {
> 	struct slave *slave;
> 	int i;
>+	struct bonding *bond = container_of(work, struct bonding,
>+					    miimon_commit_work);
>+
>+	rtnl_lock();
>+	read_lock(&bond->lock);
>
> 	bond_for_each_slave(bond, slave, i) {
> 		switch (slave->new_link) {
>@@ -2421,15 +2426,18 @@ static void bond_miimon_commit(struct bonding *bond)
> 		}
>
> do_failover:
>-		ASSERT_RTNL();
> 		write_lock_bh(&bond->curr_slave_lock);
> 		bond_select_active_slave(bond);
> 		write_unlock_bh(&bond->curr_slave_lock);
> 	}
>
> 	bond_set_carrier(bond);
>+
>+	read_unlock(&bond->lock);
>+	rtnl_unlock();
> }
>
>+
> /*
>  * bond_mii_monitor
>  *
>@@ -2438,14 +2446,13 @@ do_failover:
>  * an acquisition of appropriate locks followed by a commit phase to
>  * implement whatever link state changes are indicated.
>  */
>+
> void bond_mii_monitor(struct work_struct *work)
> {
> 	struct bonding *bond = container_of(work, struct bonding,
> 					    mii_work.work);
>
> 	read_lock(&bond->lock);
>-	if (bond->kill_timers)
>-		goto out;
>
> 	if (bond->slave_cnt == 0)
> 		goto re_arm;
>@@ -2462,23 +2469,14 @@ void bond_mii_monitor(struct work_struct *work)
> 		read_unlock(&bond->curr_slave_lock);
> 	}
>
>-	if (bond_miimon_inspect(bond)) {
>-		read_unlock(&bond->lock);
>-		rtnl_lock();
>-		read_lock(&bond->lock);
>-
>-		bond_miimon_commit(bond);
>+	if (bond_miimon_inspect(bond))
>+		queue_work(bond->wq, &bond->miimon_commit_work);
>
>-		read_unlock(&bond->lock);
>-		rtnl_unlock();	/* might sleep, hold no other locks */
>-		read_lock(&bond->lock);
>-	}
>
> re_arm:
> 	if (bond->params.miimon)
> 		queue_delayed_work(bond->wq, &bond->mii_work,
> 				   msecs_to_jiffies(bond->params.miimon));
>-out:
> 	read_unlock(&bond->lock);
> }
>
>@@ -2778,9 +2776,6 @@ void bond_loadbalance_arp_mon(struct work_struct *work)
>
> 	delta_in_ticks = msecs_to_jiffies(bond->params.arp_interval);
>
>-	if (bond->kill_timers)
>-		goto out;
>-
> 	if (bond->slave_cnt == 0)
> 		goto re_arm;
>
>@@ -2867,7 +2862,6 @@ void bond_loadbalance_arp_mon(struct work_struct *work)
> re_arm:
> 	if (bond->params.arp_interval)
> 		queue_delayed_work(bond->wq, &bond->arp_work, delta_in_ticks);
>-out:
> 	read_unlock(&bond->lock);
> }
>
>@@ -2949,13 +2943,19 @@ static int bond_ab_arp_inspect(struct bonding *bond, int delta_in_ticks)
> /*
>  * Called to commit link state changes noted by inspection step of
>  * active-backup mode ARP monitor.
>- *
>- * Called with RTNL and bond->lock for read.
>  */
>-static void bond_ab_arp_commit(struct bonding *bond, int delta_in_ticks)
>+static void bond_ab_arp_commit(struct work_struct *work)
> {
> 	struct slave *slave;
> 	int i;
>+	int delta_in_ticks;
>+	struct bonding *bond = container_of(work, struct bonding,
>+					    ab_arp_commit_work);
>+
>+	rtnl_lock();
>+	read_lock(&bond->lock);
>+
>+	delta_in_ticks = msecs_to_jiffies(bond->params.arp_interval);
>
> 	bond_for_each_slave(bond, slave, i) {
> 		switch (slave->new_link) {
>@@ -3014,6 +3014,9 @@ do_failover:
> 	}
>
> 	bond_set_carrier(bond);
>+
>+	read_unlock(&bond->lock);
>+	rtnl_unlock();
> }
>
> /*
>@@ -3093,9 +3096,6 @@ void bond_activebackup_arp_mon(struct work_struct *work)
>
> 	read_lock(&bond->lock);
>
>-	if (bond->kill_timers)
>-		goto out;
>-
> 	delta_in_ticks = msecs_to_jiffies(bond->params.arp_interval);
>
> 	if (bond->slave_cnt == 0)
>@@ -3113,24 +3113,15 @@ void bond_activebackup_arp_mon(struct work_struct *work)
> 		read_unlock(&bond->curr_slave_lock);
> 	}
>
>-	if (bond_ab_arp_inspect(bond, delta_in_ticks)) {
>-		read_unlock(&bond->lock);
>-		rtnl_lock();
>-		read_lock(&bond->lock);
>+	if (bond_ab_arp_inspect(bond, delta_in_ticks))
>+		queue_work(bond->wq, &bond->ab_arp_commit_work);
>
>-		bond_ab_arp_commit(bond, delta_in_ticks);
>-
>-		read_unlock(&bond->lock);
>-		rtnl_unlock();
>-		read_lock(&bond->lock);
>-	}
>
> 	bond_ab_arp_probe(bond);
>
> re_arm:
> 	if (bond->params.arp_interval)
> 		queue_delayed_work(bond->wq, &bond->arp_work, delta_in_ticks);
>-out:
> 	read_unlock(&bond->lock);
> }
>
>@@ -3720,8 +3711,6 @@ static int bond_open(struct net_device *bond_dev)
> {
> 	struct bonding *bond = netdev_priv(bond_dev);
>
>-	bond->kill_timers = 0;
>-
> 	if (bond_is_lb(bond)) {
> 		/* bond_alb_initialize must be called before the timer
> 		 * is started.
>@@ -3781,26 +3770,23 @@ static int bond_close(struct net_device *bond_dev)
> 	bond->send_grat_arp = 0;
> 	bond->send_unsol_na = 0;
>
>-	/* signal timers not to re-arm */
>-	bond->kill_timers = 1;
>-
> 	write_unlock_bh(&bond->lock);
>
> 	if (bond->params.miimon) {  /* link check interval, in milliseconds. */
>-		cancel_delayed_work(&bond->mii_work);
>+		cancel_delayed_work_sync(&bond->mii_work);
> 	}
>
> 	if (bond->params.arp_interval) {  /* arp interval, in milliseconds. */
>-		cancel_delayed_work(&bond->arp_work);
>+		cancel_delayed_work_sync(&bond->arp_work);
> 	}
>
> 	switch (bond->params.mode) {
> 	case BOND_MODE_8023AD:
>-		cancel_delayed_work(&bond->ad_work);
>+		cancel_delayed_work_sync(&bond->ad_work);
> 		break;
> 	case BOND_MODE_TLB:
> 	case BOND_MODE_ALB:
>-		cancel_delayed_work(&bond->alb_work);
>+		cancel_delayed_work_sync(&bond->alb_work);
> 		break;
> 	default:
> 		break;
>@@ -4660,23 +4646,19 @@ static void bond_setup(struct net_device *bond_dev)
>
> static void bond_work_cancel_all(struct bonding *bond)
> {
>-	write_lock_bh(&bond->lock);
>-	bond->kill_timers = 1;
>-	write_unlock_bh(&bond->lock);
>-
> 	if (bond->params.miimon && delayed_work_pending(&bond->mii_work))
>-		cancel_delayed_work(&bond->mii_work);
>+		cancel_delayed_work_sync(&bond->mii_work);
>
> 	if (bond->params.arp_interval && delayed_work_pending(&bond->arp_work))
>-		cancel_delayed_work(&bond->arp_work);
>+		cancel_delayed_work_sync(&bond->arp_work);
>
> 	if (bond->params.mode == BOND_MODE_ALB &&
> 	    delayed_work_pending(&bond->alb_work))
>-		cancel_delayed_work(&bond->alb_work);
>+		cancel_delayed_work_sync(&bond->alb_work);
>
> 	if (bond->params.mode == BOND_MODE_8023AD &&
> 	    delayed_work_pending(&bond->ad_work))
>-		cancel_delayed_work(&bond->ad_work);
>+		cancel_delayed_work_sync(&bond->ad_work);
> }
>
> /*
>@@ -5094,6 +5076,9 @@ static int bond_init(struct net_device *bond_dev)
> 	bond_prepare_sysfs_group(bond);
>
> 	__hw_addr_init(&bond->mc_list);
>+	INIT_WORK(&bond->miimon_commit_work, bond_miimon_commit);
>+	INIT_WORK(&bond->ab_arp_commit_work, bond_ab_arp_commit);
>+	INIT_WORK(&bond->alb_promisc_disable_work, bond_alb_promisc_disable);
> 	return 0;
> }
>
>diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
>index c6fdd85..e111023 100644
>--- a/drivers/net/bonding/bonding.h
>+++ b/drivers/net/bonding/bonding.h
>@@ -198,7 +198,6 @@ struct bonding {
> 	s32      slave_cnt; /* never change this value outside the attach/detach wrappers */
> 	rwlock_t lock;
> 	rwlock_t curr_slave_lock;
>-	s8       kill_timers;
> 	s8	 send_grat_arp;
> 	s8	 send_unsol_na;
> 	s8	 setup_by_slave;
>@@ -223,6 +222,9 @@ struct bonding {
> 	struct   delayed_work arp_work;
> 	struct   delayed_work alb_work;
> 	struct   delayed_work ad_work;
>+	struct    work_struct miimon_commit_work;
>+	struct    work_struct ab_arp_commit_work;
>+	struct    work_struct alb_promisc_disable_work;
> #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
> 	struct   in6_addr master_ipv6;
> #endif
>@@ -348,6 +350,7 @@ void bond_select_active_slave(struct bonding *bond);
> void bond_change_active_slave(struct bonding *bond, struct slave *new_active);
> void bond_register_arp(struct bonding *);
> void bond_unregister_arp(struct bonding *);
>+void bond_alb_promisc_disable(struct work_struct *work);
>
> struct bond_net {
> 	struct net *		net;	/* Associated network namespace */
>
>
>-- 
>Jiri Bohac <[email-masked]>
>SUSE Labs, SUSE CZ

---
	-Jay Vosburgh, IBM Linux Technology Center, [email-masked]