[PATCH 3.18 024/183] team: avoid possible underflow of count_pending value for notify_peers and mcast_rejoin

Greg Kroah-Hartman
2015-01-25T18:53:45Z

From: Jiri Pirko <jiri@resnulli.us>

[ Upstream commit b0d11b42785b70e19bc6a3122eead3f7969a7589 ]

This patch is fixing a race condition that may cause setting
count_pending to -1, which results in unwanted big bulk of arp messages
(in case of "notify peers").

Consider following scenario:

count_pending == 2
CPU0 CPU1
team_notify_peers_work
atomic_dec_and_test (dec count_pending to 1)
schedule_delayed_work
team_notify_peers
atomic_add (adding 1 to count_pending)
team_notify_peers_work
atomic_dec_and_test (dec count_pending to 1)
schedule_delayed_work
team_notify_peers_work
atomic_dec_and_test (dec count_pending to 0)
schedule_delayed_work
team_notify_peers_work
atomic_dec_and_test (dec count_pending to -1)

Fix this race by using atomic_dec_if_positive - that will prevent
count_pending running under 0.

Fixes: fc423ff00df3a1955441 ("team: add peer notification")
Fixes: 492b200efdd20b8fcfd ("team: add support for sending multicast rejoins")
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/team/team.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

--- a/drivers/net/team/team.c
+++ b/drivers/net/team/team.c
@@ -629,6 +629,7 @@ static int team_change_mode(struct team
static void team_notify_peers_work(struct work_struct *work)
{
struct team *team;
+ int val;

team = container_of(work, struct team, notify_peers.dw.work);

@@ -636,9 +637,14 @@ static void team_notify_peers_work(struc
schedule_delayed_work(&team->notify_peers.dw, 0);
return;
}
+ val = atomic_dec_if_positive(&team->notify_peers.count_pending);
+ if (val < 0) {
+ rtnl_unlock();
+ return;
+ }
call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, team->dev);
rtnl_unlock();
- if (!atomic_dec_and_test(&team->notify_peers.count_pending))
+ if (val)
schedule_delayed_work(&team->notify_peers.dw,
msecs_to_jiffies(team->notify_peers.interval));
}
@@ -669,6 +675,7 @@ static void team_notify_peers_fini(struc
static void team_mcast_rejoin_work(struct work_struct *work)
{
struct team *team;
+ int val;

team = container_of(work, struct team, mcast_rejoin.dw.work);

@@ -676,9 +683,14 @@ static void team_mcast_rejoin_work(struc
schedule_delayed_work(&team->mcast_rejoin.dw, 0);
return;
}
+ val = atomic_dec_if_positive(&team->mcast_rejoin.count_pending);
+ if (val < 0) {
+ rtnl_unlock();
+ return;
+ }
call_netdevice_notifiers(NETDEV_RESEND_IGMP, team->dev);
rtnl_unlock();
- if (!atomic_dec_and_test(&team->mcast_rejoin.count_pending))
+ if (val)
schedule_delayed_work(&team->mcast_rejoin.dw,
msecs_to_jiffies(team->mcast_rejoin.interval));
}