From: Victor Nogueira Date: Wed, 10 Jun 2026 13:28:24 +0000 (-0300) Subject: net/sched: sch_hfsc: Don't make class passive twice X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=90b662ea25f5e83bb3b8ccec5b93ced810b92fb8;p=thirdparty%2Flinux.git net/sched: sch_hfsc: Don't make class passive twice update_vf() is called from two places for the same class during a single dequeue when the class's child qdisc (e.g. codel/fq_codel) drops its last packets while dequeuing: 1. The child calls qdisc_tree_reduce_backlog(), which, now that the child is empty, invokes hfsc_qlen_notify() -> update_vf(cl, 0, 0) and turns the class passive (cl_nactive is decremented up the hierarchy). 2. hfsc_dequeue() then calls update_vf(cl, qdisc_pkt_len(skb), cur_time) to charge the dequeued bytes. On the second call the class is already passive, but its child qdisc is still empty, so update_vf() arms go_passive again: if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC) go_passive = 1; The leaf is then skipped by the cl_nactive == 0 check inside the loop, which does not clear go_passive, so the stale go_passive propagates to the parent and decrements its cl_nactive a second time. A parent that still has other active children is driven to cl_nactive == 0 and removed from the vttree, even though those siblings are still backlogged. They are never dequeued again and the qdisc stalls. Fix this by only arming go_passive when the class is actually active, so an already-passive class no longer triggers a second passive transition. The byte accounting (cl->cl_total += len) still runs for every ancestor, so dequeued bytes continue to be counted exactly once. Fixes: 51eb3b65544c ("sch_hfsc: make hfsc_qlen_notify() idempotent") Reported-by: Anirudh Gupta Closes: https://lore.kernel.org/netdev/CAN2cbVe79oj0O9==m4+4x3v+O+qzRagA=2=wkrp9i9=CqYvyZA@mail.gmail.com/ Tested-by: Anirudh Gupta Acked-by: Jamal Hadi Salim Signed-off-by: Victor Nogueira Link: https://patch.msgid.link/20260610132824.3027549-1-victor@mojatatu.com Signed-off-by: Jakub Kicinski --- diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c index 83b2ca2e37fc..6552c0c4e7b3 100644 --- a/net/sched/sch_hfsc.c +++ b/net/sched/sch_hfsc.c @@ -753,7 +753,7 @@ update_vf(struct hfsc_class *cl, unsigned int len, u64 cur_time) u64 f; /* , myf_bound, delta; */ int go_passive = 0; - if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC) + if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC && cl->cl_nactive) go_passive = 1; for (; cl->cl_parent != NULL; cl = cl->cl_parent) {