From: Eric Dumazet Date: Sat, 24 Aug 2024 18:19:01 +0000 (+0000) Subject: net_sched: sch_fq: fix incorrect behavior for small weights X-Git-Tag: v6.11-rc6~24^2~13 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=bc21000e99f92a6b5540d7267c6b22806c5c33d3;p=thirdparty%2Flinux.git net_sched: sch_fq: fix incorrect behavior for small weights fq_dequeue() has a complex logic to find packets in one of the 3 bands. As Neal found out, it is possible that one band has a deficit smaller than its weight. fq_dequeue() can return NULL while some packets are elligible for immediate transmit. In this case, more than one iteration is needed to refill pband->credit. With default parameters (weights 589824 196608 65536) bug can trigger if large BIG TCP packets are sent to the lowest priority band. Bisected-by: John Sperbeck Diagnosed-by: Neal Cardwell Fixes: 29f834aa326e ("net_sched: sch_fq: add 3 bands and WRR scheduling") Signed-off-by: Eric Dumazet Reviewed-by: Neal Cardwell Link: https://patch.msgid.link/20240824181901.953776-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c index 2389747256793..19a49af5a9e52 100644 --- a/net/sched/sch_fq.c +++ b/net/sched/sch_fq.c @@ -663,7 +663,9 @@ begin: pband = &q->band_flows[q->band_nr]; pband->credit = min(pband->credit + pband->quantum, pband->quantum); - goto begin; + if (pband->credit > 0) + goto begin; + retry = 0; } if (q->time_next_delayed_flow != ~0ULL) qdisc_watchdog_schedule_range_ns(&q->watchdog,