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Subject[PATCH net-next] bonding: eliminate bond_close race conditions
Date

This patch resolves two sets of race conditions.

Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com> reported the
first, as follows:

The bond_close() calls cancel_delayed_work() to cancel delayed works.
It, however, cannot cancel works that were already queued in workqueue.
The bond_open() initializes work->data, and proccess_one_work() refers
get_work_cwq(work)->wq->flags. The get_work_cwq() returns NULL when
work->data has been initialized. Thus, a panic occurs.

He included a patch that converted the cancel_delayed_work calls
in bond_close to flush_delayed_work_sync, which eliminated the above
problem.

His patch is incorporated, at least in principle, into this
patch. In this patch, we use cancel_delayed_work_sync in place of
flush_delayed_work_sync, and also convert bond_uninit in addition to
bond_close.

This conversion to _sync, however, opens new races between
bond_close and three periodically executing workqueue functions:
bond_mii_monitor, bond_alb_monitor and bond_activebackup_arp_mon.

The race occurs because bond_close and bond_uninit are always
called with RTNL held, and these workqueue functions may acquire RTNL to
perform failover-related activities. If bond_close or bond_uninit is
waiting in cancel_delayed_work_sync, deadlock occurs.

These deadlocks are resolved by having the workqueue functions
acquire RTNL conditionally. If the rtnl_trylock() fails, the functions
reschedule and return immediately. For the cases that are attempting to
perform link failover, a delay of 1 is used; for the other cases, the
normal interval is used (as those activities are not as time critical).

Additionally, the bond_mii_monitor function now stores the delay
in a variable (mimicing the structure of activebackup_arp_mon).

Lastly, all of the above renders the kill_timers sentinel moot,
and therefore it has been removed.

Tested-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>

---
drivers/net/bonding/bond_3ad.c | 8 +---
drivers/net/bonding/bond_alb.c | 16 +++----
drivers/net/bonding/bond_main.c | 96 +++++++++++++++++++++------------------
drivers/net/bonding/bonding.h | 1 -
4 files changed, 61 insertions(+), 60 deletions(-)
diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
index b33c099..0ae0d7c 100644
--- a/drivers/net/bonding/bond_3ad.c
+++ b/drivers/net/bonding/bond_3ad.c
@@ -2110,9 +2110,6 @@ 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;
@@ -2161,9 +2158,8 @@ void bond_3ad_state_machine_handler(struct work_struct *work)
}

re_arm:
- if (!bond->kill_timers)
- queue_delayed_work(bond->wq, &bond->ad_work, ad_delta_in_ticks);
-out:
+ queue_delayed_work(bond->wq, &bond->ad_work, ad_delta_in_ticks);
+
read_unlock(&bond->lock);
}

diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
index d4fbd2e..106b88a 100644
--- a/drivers/net/bonding/bond_alb.c
+++ b/drivers/net/bonding/bond_alb.c
@@ -1343,10 +1343,6 @@ 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;
@@ -1401,10 +1397,13 @@ void bond_alb_monitor(struct work_struct *work)

/*
* dev_set_promiscuity requires rtnl and
- * nothing else.
+ * nothing else. Avoid race with bond_close.
*/
read_unlock(&bond->lock);
- rtnl_lock();
+ if (!rtnl_trylock()) {
+ read_lock(&bond->lock);
+ goto re_arm;
+ }

bond_info->rlb_promisc_timeout_counter = 0;

@@ -1440,9 +1439,8 @@ void bond_alb_monitor(struct work_struct *work)
}

re_arm:
- if (!bond->kill_timers)
- queue_delayed_work(bond->wq, &bond->alb_work, alb_delta_in_ticks);
-out:
+ queue_delayed_work(bond->wq, &bond->alb_work, alb_delta_in_ticks);
+
read_unlock(&bond->lock);
}

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 71efff3..9931a16 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -774,9 +774,6 @@ static void bond_resend_igmp_join_requests(struct bonding *bond)

read_lock(&bond->lock);

- if (bond->kill_timers)
- goto out;
-
/* rejoin all groups on bond device */
__bond_resend_igmp_join_requests(bond->dev);

@@ -790,9 +787,9 @@ static void bond_resend_igmp_join_requests(struct bonding *bond)
__bond_resend_igmp_join_requests(vlan_dev);
}

- if ((--bond->igmp_retrans > 0) && !bond->kill_timers)
+ if (--bond->igmp_retrans > 0)
queue_delayed_work(bond->wq, &bond->mcast_work, HZ/5);
-out:
+
read_unlock(&bond->lock);
}

@@ -2518,10 +2515,11 @@ void bond_mii_monitor(struct work_struct *work)
struct bonding *bond = container_of(work, struct bonding,
mii_work.work);
bool should_notify_peers = false;
+ unsigned long delay;

read_lock(&bond->lock);
- if (bond->kill_timers)
- goto out;
+
+ delay = msecs_to_jiffies(bond->params.miimon);

if (bond->slave_cnt == 0)
goto re_arm;
@@ -2530,7 +2528,15 @@ void bond_mii_monitor(struct work_struct *work)

if (bond_miimon_inspect(bond)) {
read_unlock(&bond->lock);
- rtnl_lock();
+
+ /* Race avoidance with bond_close cancel of workqueue */
+ if (!rtnl_trylock()) {
+ read_lock(&bond->lock);
+ delay = 1;
+ should_notify_peers = false;
+ goto re_arm;
+ }
+
read_lock(&bond->lock);

bond_miimon_commit(bond);
@@ -2541,14 +2547,18 @@ void bond_mii_monitor(struct work_struct *work)
}

re_arm:
- if (bond->params.miimon && !bond->kill_timers)
- queue_delayed_work(bond->wq, &bond->mii_work,
- msecs_to_jiffies(bond->params.miimon));
-out:
+ if (bond->params.miimon)
+ queue_delayed_work(bond->wq, &bond->mii_work, delay);
+
read_unlock(&bond->lock);

if (should_notify_peers) {
- rtnl_lock();
+ if (!rtnl_trylock()) {
+ read_lock(&bond->lock);
+ bond->send_peer_notif++;
+ read_unlock(&bond->lock);
+ return;
+ }
netdev_bonding_change(bond->dev, NETDEV_NOTIFY_PEERS);
rtnl_unlock();
}
@@ -2790,9 +2800,6 @@ 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;

@@ -2889,9 +2896,9 @@ void bond_loadbalance_arp_mon(struct work_struct *work)
}

re_arm:
- if (bond->params.arp_interval && !bond->kill_timers)
+ if (bond->params.arp_interval)
queue_delayed_work(bond->wq, &bond->arp_work, delta_in_ticks);
-out:
+
read_unlock(&bond->lock);
}

@@ -3132,9 +3139,6 @@ 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)
@@ -3144,7 +3148,15 @@ void bond_activebackup_arp_mon(struct work_struct *work)

if (bond_ab_arp_inspect(bond, delta_in_ticks)) {
read_unlock(&bond->lock);
- rtnl_lock();
+
+ /* Race avoidance with bond_close flush of workqueue */
+ if (!rtnl_trylock()) {
+ read_lock(&bond->lock);
+ delta_in_ticks = 1;
+ should_notify_peers = false;
+ goto re_arm;
+ }
+
read_lock(&bond->lock);

bond_ab_arp_commit(bond, delta_in_ticks);
@@ -3157,13 +3169,18 @@ void bond_activebackup_arp_mon(struct work_struct *work)
bond_ab_arp_probe(bond);

re_arm:
- if (bond->params.arp_interval && !bond->kill_timers)
+ if (bond->params.arp_interval)
queue_delayed_work(bond->wq, &bond->arp_work, delta_in_ticks);
-out:
+
read_unlock(&bond->lock);

if (should_notify_peers) {
- rtnl_lock();
+ if (!rtnl_trylock()) {
+ read_lock(&bond->lock);
+ bond->send_peer_notif++;
+ read_unlock(&bond->lock);
+ return;
+ }
netdev_bonding_change(bond->dev, NETDEV_NOTIFY_PEERS);
rtnl_unlock();
}
@@ -3425,8 +3442,6 @@ static int bond_open(struct net_device *bond_dev)
struct slave *slave;
int i;

- bond->kill_timers = 0;
-
/* reset slave->backup and slave->inactive */
read_lock(&bond->lock);
if (bond->slave_cnt > 0) {
@@ -3495,33 +3510,30 @@ static int bond_close(struct net_device *bond_dev)

bond->send_peer_notif = 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;
}

if (delayed_work_pending(&bond->mcast_work))
- cancel_delayed_work(&bond->mcast_work);
+ cancel_delayed_work_sync(&bond->mcast_work);

if (bond_is_lb(bond)) {
/* Must be called only after all
@@ -4368,26 +4380,22 @@ 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);

if (delayed_work_pending(&bond->mcast_work))
- cancel_delayed_work(&bond->mcast_work);
+ cancel_delayed_work_sync(&bond->mcast_work);
}

/*
diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
index 82fec5f..1aecc37 100644
--- a/drivers/net/bonding/bonding.h
+++ b/drivers/net/bonding/bonding.h
@@ -222,7 +222,6 @@ struct bonding {
struct slave *);
rwlock_t lock;
rwlock_t curr_slave_lock;
- s8 kill_timers;
u8 send_peer_notif;
s8 setup_by_slave;
s8 igmp_retrans;
--
1.7.1


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