6.10-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit bc21000e99f92a6b5540d7267c6b22806c5c33d3 ]
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 <jsperbeck@xxxxxxxxxx>
Diagnosed-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Fixes: 29f834aa326e ("net_sched: sch_fq: add 3 bands and WRR scheduling")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Link: https://patch.msgid.link/20240824181901.953776-1-edumazet@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 2389747256793..19a49af5a9e52 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -663,7 +663,9 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
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,
--
2.43.0
