Re: Packet gets stuck in NOLOCK pfifo_fast qdisc

[Jonas Bonn]

Hi Cong,

On 01/07/2020 21:58, Cong Wang wrote:
> On Wed, Jul 1, 2020 at 9:05 AM Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
> > On Tue, Jun 30, 2020 at 2:08 PM Josh Hunt <johunt@xxxxxxxxxx> wrote:
> > > Do either of you know if there's been any development on a fix for this
> > > issue? If not we can propose something.
> >
> > If you have a reproducer, I can look into this.
>
> Does the attached patch fix this bug completely?

It's easier to comment if you inline the patch, but after taking a quick 
look it seems too simplistic.

i)  Are you sure you haven't got the return values on qdisc_run reversed?
ii) There's a "bypass" path that skips the enqueue/dequeue operation if 
the queue is empty; that needs a similar treatment:  after releasing 
seqlock it needs to ensure that another packet hasn't been enqueued 
since it last checked.

/Jonas

> Thanks.