ifb: fix rcu_sched self-detected stalls

ifb: fix rcu_sched self-detected stalls

[ Upstream commit 440d57bc5ff55ec1efb3efc9cbe9420b4bbdfefa ]

According to the commit 16b0dc29c1af9df341428f4c49ada4f626258082
(dummy: fix rcu_sched self-detected stalls)

Eric Dumazet fix the problem in dummy, but the ifb will occur the
same problem like the dummy modules.

Trying to "modprobe ifb numifbs=30000" triggers :

INFO: rcu_sched self-detected stall on CPU

After this splat, RTNL is locked and reboot is needed.

We must call cond_resched() to avoid this, even holding RTNL.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[wt: 2.6.32: cond_resched() needs linux/sched.h]
Signed-off-by: Willy Tarreau <w@1wt.eu>