bonding: eliminate bond_close race conditions

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 9 deletions

diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
index d4fbd2e6261..106b88a0473 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);
 }