Re: [PATCH RESEND net-next 2/5] net/sched: taprio: keep child Qdisc refcount elevated at 2 in offload mode

[Vladimir Oltean]

On Wed, Jun 07, 2023 at 12:05:19PM +0200, Paolo Abeni wrote:
> Perhaps the above chunk could be:
> 
> 	*old = q->qdiscs[cl - 1];
> 	if (FULL_OFFLOAD_IS_ENABLED(q->flags)) {
> 		WARN_ON_ONCE(dev_graft_qdisc(dev_queue, new) != *old);
> 		if (new)
> 			qdisc_refcount_inc(new);
> 		if (*old)
> 			qdisc_put(*old);
> 	}
> 
> (boldly assuming I'm not completely lost, which looks a wild bet ;)

Yeah, could be like that. In full offload mode, q->qdiscs[cl - 1] is
also what's grafted to the TXQ, so the WARN_ON() would be indicative of
a serious bug if it triggered.

> > > BTW, what about including your tests from the cover letter somewhere under tc-testing?
> > 
> > I don't know about that. Does it involve adding taprio hw offload to netdevsim,
> > so that both code paths are covered?
> 
> I guess I underlooked the needed effort and we could live without new
> tests here.

Let's see how the discussion progresses.