| Message ID | 20241125174608.1484356-1-martin.ottens@fau.de (mailing list archive) |
|---|---|
| State | New |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [v2] net/sched: tbf: correct backlog statistic for GSO packets | expand |
On Mon, Nov 25, 2024 at 6:46 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. > > Fixes: e43ac79a4bc6 ("sch_tbf: segment too big GSO packets") > Signed-off-by: Martin Ottens <martin.ottens@fau.de> This seems fine, please note we ask for a 24 hours delay between each version, to let other reviewers chime in. Reviewed-by: Eric Dumazet <edumazet@google.com> Can you also take a look at net/sched/sch_taprio.c, it seems the bug has been copy/pasted there as well.
diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c index f1d09183ae63..dc26b22d53c7 100644 --- a/net/sched/sch_tbf.c +++ b/net/sched/sch_tbf.c @@ -208,7 +208,7 @@ static int tbf_segment(struct sk_buff *skb, struct Qdisc *sch, struct tbf_sched_data *q = qdisc_priv(sch); struct sk_buff *segs, *nskb; netdev_features_t features = netif_skb_features(skb); - unsigned int len = 0, prev_len = qdisc_pkt_len(skb); + unsigned int len = 0, prev_len = qdisc_pkt_len(skb), seg_len; int ret, nb; segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK); @@ -219,21 +219,27 @@ static int tbf_segment(struct sk_buff *skb, struct Qdisc *sch, nb = 0; skb_list_walk_safe(segs, segs, nskb) { skb_mark_not_on_list(segs); - qdisc_skb_cb(segs)->pkt_len = segs->len; - len += segs->len; + seg_len = segs->len; + qdisc_skb_cb(segs)->pkt_len = seg_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 += seg_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; + consume_skb(skb); + return NET_XMIT_SUCCESS; + } + + kfree_skb(skb); + return NET_XMIT_DROP; } static int tbf_enqueue(struct sk_buff *skb, struct Qdisc *sch,
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. Fixes: e43ac79a4bc6 ("sch_tbf: segment too big GSO packets") Signed-off-by: Martin Ottens <martin.ottens@fau.de> --- net/sched/sch_tbf.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-)