From bc21000e99f92a6b5540d7267c6b22806c5c33d3 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sat, 24 Aug 2024 18:19:01 +0000 Subject: [PATCH] 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 --- net/sched/sch_fq.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c index 238974725679..19a49af5a9e5 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,