netdev - "lockless" qdisc breaks tx_queue

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Date:   Tue, 2 Jan 2018 20:41:20 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: "lockless" qdisc breaks tx_queue_len change too?

Hi, John

While reviewing your ptr_ring fix again today, it looks like your
"lockless" qdisc patchset breaks dev->tx_queue_len behavior.

Before your patchset, dev->tx_queue_len is merely an integer to read,
after your patchset, the skb array has to be resized when
dev->tx_queue_len changes, but I don't see any qdisc code handles
this...

Also, because of that, I doubt __skb_array_empty() in
pfifo_fast_dequeue() can be safe any more even with your ptr_ring fix.

What am I missing?

Thanks.