Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting

On Tue, May 16, 2023 at 02:50:10PM -0700, Jakub Kicinski wrote:

quoted

quoted

Vlad, could you please clarify how you expect the unlocked filter
operations to work when the qdisc has global state?  

Jakub, I didn't account for per-net_device pointer usage by miniqp code
hence this bug. I didn't comment on the fix because I was away from my
PC last week but Peilin's approach seems reasonable to me. When Peilin
brought up the issue initially I also tried to come up with some trick
to contain the changes to miniqp code instead of changing core but
couldn't think of anything workable due to the limitations already
discussed in this thread. I'm open to explore alternative approaches to
solving this issue, if that is what you suggest.

Given Peilin's investigation I think fix without changing core may
indeed be hard. I'm not sure if returning -EBUSY when qdisc refcnt
is elevated will be appreciated by the users, do we already have
similar behavior in other parts of TC?

Seems like trying to delete an "in-use" cls_u32 filter returns -EBUSY:

net/sched/cls_u32.c:

	if (ht->refcnt == 1) {
		u32_destroy_hnode(tp, ht, extack);
	} else {
		NL_SET_ERR_MSG_MOD(extack, "Can not delete in-use filter");
		return -EBUSY;
	}

Thanks,
Peilin Ye