The 4-state Markov chain in loss_4state() has gaps at the boundaries between transition probability ranges. The comparisons use: if (rnd < a4) else if (a4 < rnd && rnd < a1 + a4) When rnd equals a boundary value exactly, neither branch matches and no state transition occurs. The redundant lower-bound check (a4 < rnd) is already implied by being in the else branch. Remove the unnecessary lower-bound comparisons so the ranges are contiguous and every random value produces a transition, matching the GI (General and Intuitive) loss model specification. This bug goes back to original implementation of this model. Fixes: 661b79725fea ("netem: revised correlated loss generator") Signed-off-by: Stephen Hemminger --- 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 08006a60849e..00ece854280a 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -237,7 +237,7 @@ static bool loss_4state(struct netem_sched_data *q) if (rnd < clg->a4) { clg->state = LOST_IN_GAP_PERIOD; return true; - } else if (clg->a4 < rnd && rnd < clg->a1 + clg->a4) { + } else if (rnd < clg->a1 + clg->a4) { clg->state = LOST_IN_BURST_PERIOD; return true; } else if (clg->a1 + clg->a4 < rnd) { @@ -257,7 +257,7 @@ static bool loss_4state(struct netem_sched_data *q) case LOST_IN_BURST_PERIOD: if (rnd < clg->a3) clg->state = TX_IN_BURST_PERIOD; - else if (clg->a3 < rnd && rnd < clg->a2 + clg->a3) { + else if (rnd < clg->a2 + clg->a3) { clg->state = TX_IN_GAP_PERIOD; } else if (clg->a2 + clg->a3 < rnd) { clg->state = LOST_IN_BURST_PERIOD; -- 2.51.0