On 2021/3/17 2:43, Cong Wang wrote:
On Mon, Mar 15, 2021 at 4:42 PM David Miller <davem@redhat.com> wrote:
From: Yunsheng Lin <linyunsheng@huawei.com> Date: Mon, 15 Mar 2021 17:30:10 +0800
Currently qdisc_lock(q) is taken before enqueuing and dequeuing for lockless qdisc's skb_bad_txq/gso_skb queue, qdisc->seqlock is also taken, which can provide the same protection as qdisc_lock(q).
This patch removes the unnecessay qdisc_lock(q) protection for lockless qdisc' skb_bad_txq/gso_skb queue.
And dev_reset_queue() takes the qdisc->seqlock for lockless qdisc besides taking the qdisc_lock(q) when doing the qdisc reset, some_qdisc_is_busy() takes both qdisc->seqlock and qdisc_lock(q) when checking qdisc status. It is unnecessary to take both lock while the fast path only take one lock, so this patch also changes it to only take qdisc_lock(q) for locked qdisc, and only take qdisc->seqlock for lockless qdisc.
Since qdisc->seqlock is taken for lockless qdisc when calling qdisc_is_running() in some_qdisc_is_busy(), use qdisc->running to decide if the lockless qdisc is running.
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
What about other things protected by this lock, such as statistics and qlen?
This change looks too risky to me.
They are per-cpu for pfifo_fast which sets TCQ_F_CPUSTATS too.
Did you mean qdisc_lock(q) are protecting per-cpu stats for pfifo_fast too?
Thanks.
.