On Tue, May 30, 2023 at 03:18:19PM +0300, Vlad Buslov wrote:

quoted

quoted

If livelock with concurrent filters insertion is an issue, then it can
be remedied by setting a new Qdisc->flags bit
"DELETED-REJECT-NEW-FILTERS" and checking for it together with
QDISC_CLASS_OPS_DOIT_UNLOCKED in order to force any concurrent filter
insertion coming after the flag is set to synchronize on rtnl lock.

Thanks for the suggestion!  I'll try this approach.

Currently QDISC_CLASS_OPS_DOIT_UNLOCKED is checked after taking a refcnt of
the "being-deleted" Qdisc.  I'll try forcing "late" requests (that arrive
later than Qdisc is flagged as being-deleted) sync on RTNL lock without
(before) taking the Qdisc refcnt (otherwise I think Task 1 will replay for
even longer?).

Yeah, I see what you mean. Looking at the code __tcf_qdisc_find()
already returns -EINVAL when q->refcnt is zero, so maybe returning
-EINVAL from that function when "DELETED-REJECT-NEW-FILTERS" flags is
set is also fine? Would be much easier to implement as opposed to moving
rtnl_lock there.

Ah, I see, sure.

Thanks,
Peilin Ye