From: Peilin Ye peilin.ye@bytedance.com
[ Upstream commit a2b1a5d40bd12b44322c2ccd40bb0ec1699708b6 ]
As reported by Yuming, currently tc always show a latency of UINT_MAX for netem Qdisc's on 32-bit platforms:
$ tc qdisc add dev dummy0 root netem latency 100ms $ tc qdisc show dev dummy0 qdisc netem 8001: root refcnt 2 limit 1000 delay 275s 275s ^^^^^^^^^^^^^^^^
Let us take a closer look at netem_dump():
qopt.latency = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->latency, UINT_MAX);
qopt.latency is __u32, psched_tdiff_t is signed long, (psched_tdiff_t)(UINT_MAX) is negative for 32-bit platforms, so qopt.latency is always UINT_MAX.
Fix it by using psched_time_t (u64) instead.
Note: confusingly, users have two ways to specify 'latency':
1. normally, via '__u32 latency' in struct tc_netem_qopt; 2. via the TCA_NETEM_LATENCY64 attribute, which is s64.
For the second case, theoretically 'latency' could be negative. This patch ignores that corner case, since it is broken (i.e. assigning a negative s64 to __u32) anyways, and should be handled separately.
Thanks Ted Lin for the analysis [1] .
[1] https://github.com/raspberrypi/linux/issues/3512
Reported-by: Yuming Chen chenyuming.junnan@bytedance.com Fixes: 112f9cb65643 ("netem: convert to qdisc_watchdog_schedule_ns") Reviewed-by: Cong Wang cong.wang@bytedance.com Signed-off-by: Peilin Ye peilin.ye@bytedance.com Acked-by: Stephen Hemminger stephen@networkplumber.org Link: https://lore.kernel.org/r/20220616234336.2443-1-yepeilin.cs@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/sched/sch_netem.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index f4101a920d1f..1802f134aa40 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -1146,9 +1146,9 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb) struct tc_netem_rate rate; struct tc_netem_slot slot;
- qopt.latency = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->latency), + qopt.latency = min_t(psched_time_t, PSCHED_NS2TICKS(q->latency), UINT_MAX); - qopt.jitter = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->jitter), + qopt.jitter = min_t(psched_time_t, PSCHED_NS2TICKS(q->jitter), UINT_MAX); qopt.limit = q->limit; qopt.loss = q->loss;