Re: [PATCH] net/sched: use spin_lock_bh() on &gact->tcf_lock

[Chengfeng Ye]

Hi Jakub,

Thanks for the reply,

I inspected the code a bit more, it seems that the TC action is called from
tcf_proto_ops.classify() callback, which is called from Qdisc_ops enqueue
callback.

Then Qdisc enqueue callback is from

-> __dev_queue_xmit()
-> __dev_xmit_skb()
-> dev_qdisc_enqueue()

inside the net core. It seems that this __dev_queue_xmit() callback is
typically called from BH context (e.g.,  NET_TX_SOFTIRQ) with BH
already disabled, but sometimes also can from a work queue under
process context, one case is the br_mrp_test_work_expired() inside
net/bridge/br_mrp.c. Does it indicate that this TC action could also be
called with BH enable? I am not a developer so really not sure about it,
as the networking code is a bit long and complicated.

Thanks again,
Chengfeng