Hi Hillf,
I just tried the updated version and the system can boot up now.
It does mitigate the issue a lot but still couldn't get rid of it
thoroughly. It seems to me like the effect of Cong's patch.
Hillf Danton <hdan...@sina.com> 于2020年8月25日周二 上午11:23写道：
>
>
> Hi Feng,
>
> On Tue, 25 Aug 2020 10:18:05 +0800 Fengkehuan Feng wrote:
> > Hillf,
> >
> > With the latest version (attached what I have changed on my tree), the
> > system failed to start up with cpu stalled.
>
> My fault.
>
> There is a missing break while running qdisc and it's fixed
> in the diff below for Linux-5.x.
>
> If it is Linux-4.x in your testing, running qdisc looks a bit
> different based on your diff(better if it's in the message body):
>
> static inline void qdisc_run(struct Qdisc *q)
> {
> - if (qdisc_run_begin(q)) {
> + while (qdisc_run_begin(q)) {
> + int seq = q->pkt_seq;
> __qdisc_run(q);
> qdisc_run_end(q);
> +
> + /* go another round if there are pkts enqueued after
> + * taking seq_lock
> + */
> + if (seq != q->pkt_seq)
> + continue;
> + else
> + return;
> }
> }
>
>
> Hillf
>
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -79,6 +79,7 @@ struct Qdisc {
> #define TCQ_F_INVISIBLE 0x80 /* invisible by default in dump
> */
> #define TCQ_F_NOLOCK 0x100 /* qdisc does not require locking */
> #define TCQ_F_OFFLOADED 0x200 /* qdisc is offloaded to HW */
> + int pkt_seq;
> u32 limit;
> const struct Qdisc_ops *ops;
> struct qdisc_size_table __rcu *stab;
> --- a/net/sched/sch_generic.c
> +++ b/net/sched/sch_generic.c
> @@ -631,6 +631,7 @@ static int pfifo_fast_enqueue(struct sk_
> return qdisc_drop(skb, qdisc, to_free);
> }
>
> + qdisc->pkt_seq++;
> qdisc_update_stats_at_enqueue(qdisc, pkt_len);
> return NET_XMIT_SUCCESS;
> }
> --- a/include/net/pkt_sched.h
> +++ b/include/net/pkt_sched.h
> @@ -117,14 +117,27 @@ void __qdisc_run(struct Qdisc *q);
>
> static inline void qdisc_run(struct Qdisc *q)
> {
> - if (qdisc_run_begin(q)) {
> + while (qdisc_run_begin(q)) {
> + int seq = q->pkt_seq;
> + bool check_seq = false;
> +
> /* NOLOCK qdisc must check 'state' under the qdisc seqlock
> * to avoid racing with dev_qdisc_reset()
> */
> if (!(q->flags & TCQ_F_NOLOCK) ||
> - likely(!test_bit(__QDISC_STATE_DEACTIVATED, &q->state)))
> + likely(!test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) {
> __qdisc_run(q);
> + check_seq = true;
> + }
> qdisc_run_end(q);
> +
> + /* go another round if there are pkts enqueued after
> + * taking seq_lock
> + */
> + if (check_seq && seq != q->pkt_seq)
> + continue;
> + else
> + return;
> }
> }
>
> --
>
