[Linuxarm] Re: [PATCH net v8 1/3] net: sched: fix packet stuck problem for lockless qdisc

On Fri, 14 May 2021 16:36:16 -0700 Cong Wang wrote:

...

@@ -176,8 +202,15 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc) static inline void qdisc_run_end(struct Qdisc *qdisc) { write_seqcount_end(&qdisc->running);

•   if (qdisc->flags & TCQ_F_NOLOCK)
  

•   if (qdisc->flags & TCQ_F_NOLOCK) {
            spin_unlock(&qdisc->seqlock);
  

•           if (unlikely(test_bit(__QDISC_STATE_MISSED,
  

•                                 &qdisc->state))) {
  

•                   clear_bit(__QDISC_STATE_MISSED, &qdisc->state);  
  

We have test_and_clear_bit() which is atomic, test_bit()+clear_bit() is not.

It doesn't have to be atomic, right? I asked to split the test because test_and_clear is a locked op on x86, test by itself is not.