[PATCH] cgroup: fix panic in netprio_cgroup

[Gao feng <gaofeng@cn.fujitsu.com>]

we set max_prioidx to the first zero bit index of prioidx_map in
function get_prioidx.

So when we delete the low index netprio cgroup and adding a new
netprio cgroup again,the max_prioidx will be set to the low index.

when we set the high index cgroup's net_prio.ifpriomap,the function
write_priomap will call update_netdev_tables to alloc memory which
size is sizeof(struct netprio_map) + sizeof(u32) * (max_prioidx + 1),
so the size of array that map->priomap point to is max_prioidx +1,
which is low than what we actually need.

fix this by adding check in get_prioidx,only set max_prioidx when
max_prioidx low than the new prioidx.

Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
---
 net/core/netprio_cgroup.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index 5b8aa2f..586f7d9 100644
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c
@@ -50,7 +50,8 @@ static int get_prioidx(u32 *prio)
 	}
 	set_bit(prioidx, prioidx_map);
 	spin_unlock_irqrestore(&prioidx_map_lock, flags);
-	atomic_set(&max_prioidx, prioidx);
+	if (atomic_read(&max_prioidx) < prioidx)
+		atomic_set(&max_prioidx, prioidx);
 	*prio = prioidx;
 	return 0;
 }
-- 
1.7.7.6