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Subject[PATCH 3.13 025/162] team: avoid race condition in scheduling delayed work
Date
3.13.11.11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Lawrence <Joe.Lawrence@stratus.com>

[ Upstream commit 47549650abd13d873fd2e5fc218db19e21031074 ]

When team_notify_peers and team_mcast_rejoin are called, they both reset
their respective .count_pending atomic variable. Then when the actual
worker function is executed, the variable is atomically decremented.
This pattern introduces a potential race condition where the
.count_pending rolls over and the worker function keeps rescheduling
until .count_pending decrements to zero again:

THREAD 1 THREAD 2

======== ========
team_notify_peers(teamX)
atomic_set count_pending = 1
schedule_delayed_work
team_notify_peers(teamX)
atomic_set count_pending = 1
team_notify_peers_work
atomic_dec_and_test
count_pending = 0
(return)
schedule_delayed_work
team_notify_peers_work
atomic_dec_and_test
count_pending = -1
schedule_delayed_work
(repeat until count_pending = 0)

Instead of assigning a new value to .count_pending, use atomic_add to
tack-on the additional desired worker function invocations.

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Fixes: fc423ff00df3a19554414ee ("team: add peer notification")
Fixes: 492b200efdd20b8fcfdac87 ("team: add support for sending multicast rejoins")
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
drivers/net/team/team.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c
index 99500d1..2898c2a 100644
--- a/drivers/net/team/team.c
+++ b/drivers/net/team/team.c
@@ -647,7 +647,7 @@ static void team_notify_peers(struct team *team)
{
if (!team->notify_peers.count || !netif_running(team->dev))
return;
- atomic_set(&team->notify_peers.count_pending, team->notify_peers.count);
+ atomic_add(team->notify_peers.count, &team->notify_peers.count_pending);
schedule_delayed_work(&team->notify_peers.dw, 0);
}

@@ -687,7 +687,7 @@ static void team_mcast_rejoin(struct team *team)
{
if (!team->mcast_rejoin.count || !netif_running(team->dev))
return;
- atomic_set(&team->mcast_rejoin.count_pending, team->mcast_rejoin.count);
+ atomic_add(team->mcast_rejoin.count, &team->mcast_rejoin.count_pending);
schedule_delayed_work(&team->mcast_rejoin.dw, 0);
}

--
1.9.1


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