| Message ID | 20241125131356.932264-1-martin.ottens@fau.de (mailing list archive) |
|---|---|
| State | New |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net/sched: tbf: correct backlog statistic for GSO packets | expand |
On Mon, Nov 25, 2024 at 2:14 PM Martin Ottens <martin.ottens@fau.de> wrote: > > When the length of a GSO packet in the tbf qdisc is larger than the burst > size configured the packet will be segmented by the tbf_segment function. > Whenever this function is used to enqueue SKBs, the backlog statistic of > the tbf is not increased correctly. This can lead to underflows of the > 'backlog' byte-statistic value when these packets are dequeued from tbf. > > Reproduce the bug: > Ensure that the sender machine has GSO enabled. Configured the tbf on > the outgoing interface of the machine as follows (burstsize = 1 MTU): > $ tc qdisc add dev <oif> root handle 1: tbf rate 50Mbit burst 1514 latency 50ms > > Send bulk TCP traffic out via this interface, e.g., by running an iPerf3 > client on this machine. Check the qdisc statistics: > $ tc -s qdisc show dev <oif> > > The 'backlog' byte-statistic has incorrect values while traffic is > transferred, e.g., high values due to u32 underflows. When the transfer > is stopped, the value is != 0, which should never happen. > > This patch fixes this bug by updating the statistics correctly, even if > single SKBs of a GSO SKB cannot be enqueued. > > Signed-off-by: Martin Ottens <martin.ottens@fau.de> Please add a Fixe: tag. I think this would be Fixes: e43ac79a4bc6 ("sch_tbf: segment too big GSO packets") > --- > net/sched/sch_tbf.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c > index f1d09183ae63..ef7752f9d0d9 100644 > --- a/net/sched/sch_tbf.c > +++ b/net/sched/sch_tbf.c > @@ -220,17 +220,18 @@ static int tbf_segment(struct sk_buff *skb, struct Qdisc *sch, > skb_list_walk_safe(segs, segs, nskb) { > skb_mark_not_on_list(segs); > qdisc_skb_cb(segs)->pkt_len = segs->len; > - len += segs->len; > ret = qdisc_enqueue(segs, q->qdisc, to_free); > if (ret != NET_XMIT_SUCCESS) { > if (net_xmit_drop_count(ret)) > qdisc_qstats_drop(sch); > } else { > nb++; > + len += segs->len; I do not think it is safe to access segs->len after qdisc_enqueue() : We lost ownership of segs already. I would store the segs->len in a temporary variable before calling qdisc_enqueue() > } > } > sch->q.qlen += nb; > - if (nb > 1) > + sch->qstats.backlog += len; > + if (nb > 0) > qdisc_tree_reduce_backlog(sch, 1 - nb, prev_len - len); > consume_skb(skb); We might also call kfree_skb(skb) instead of consume_skb() if nb == 0 > return nb > 0 ? NET_XMIT_SUCCESS : NET_XMIT_DROP; > -- > 2.39.5 >
diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c index f1d09183ae63..ef7752f9d0d9 100644 --- a/net/sched/sch_tbf.c +++ b/net/sched/sch_tbf.c @@ -220,17 +220,18 @@ static int tbf_segment(struct sk_buff *skb, struct Qdisc *sch, skb_list_walk_safe(segs, segs, nskb) { skb_mark_not_on_list(segs); qdisc_skb_cb(segs)->pkt_len = segs->len; - len += segs->len; ret = qdisc_enqueue(segs, q->qdisc, to_free); if (ret != NET_XMIT_SUCCESS) { if (net_xmit_drop_count(ret)) qdisc_qstats_drop(sch); } else { nb++; + len += segs->len; } } sch->q.qlen += nb; - if (nb > 1) + sch->qstats.backlog += len; + if (nb > 0) qdisc_tree_reduce_backlog(sch, 1 - nb, prev_len - len); consume_skb(skb); return nb > 0 ? NET_XMIT_SUCCESS : NET_XMIT_DROP;
When the length of a GSO packet in the tbf qdisc is larger than the burst size configured the packet will be segmented by the tbf_segment function. Whenever this function is used to enqueue SKBs, the backlog statistic of the tbf is not increased correctly. This can lead to underflows of the 'backlog' byte-statistic value when these packets are dequeued from tbf. Reproduce the bug: Ensure that the sender machine has GSO enabled. Configured the tbf on the outgoing interface of the machine as follows (burstsize = 1 MTU): $ tc qdisc add dev <oif> root handle 1: tbf rate 50Mbit burst 1514 latency 50ms Send bulk TCP traffic out via this interface, e.g., by running an iPerf3 client on this machine. Check the qdisc statistics: $ tc -s qdisc show dev <oif> The 'backlog' byte-statistic has incorrect values while traffic is transferred, e.g., high values due to u32 underflows. When the transfer is stopped, the value is != 0, which should never happen. This patch fixes this bug by updating the statistics correctly, even if single SKBs of a GSO SKB cannot be enqueued. Signed-off-by: Martin Ottens <martin.ottens@fau.de> --- net/sched/sch_tbf.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)