The rcu_barrier_bh() in mini_qdisc_pair_swap() is to wait for flying RCU callback installed by a previous mini_qdisc_pair_swap(), however we miss it on the tp_head==NULL path, which leads to that the RCU callback still uses miniq_old->rcu after it is freed together with qdisc in qdisc_graft(). So just add it on that path too.
Fixes: 46209401f8f6 ("net: core: introduce mini_Qdisc and eliminate usage of tp->q for clsact fastpath ") Reported-by: Jakub Kicinski <jakub.kicin...@netronome.com> Tested-by: Jakub Kicinski <jakub.kicin...@netronome.com> Cc: Jiri Pirko <j...@mellanox.com> Cc: John Fastabend <john.fastab...@gmail.com> Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com> --- net/sched/sch_generic.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index cd1b200acae7..661c7144b53a 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -1040,6 +1040,8 @@ void mini_qdisc_pair_swap(struct mini_Qdisc_pair *miniqp, if (!tp_head) { RCU_INIT_POINTER(*miniqp->p_miniq, NULL); + /* Wait for flying RCU callback before it is freed. */ + rcu_barrier_bh(); return; } @@ -1055,7 +1057,7 @@ void mini_qdisc_pair_swap(struct mini_Qdisc_pair *miniqp, rcu_assign_pointer(*miniqp->p_miniq, miniq); if (miniq_old) - /* This is counterpart of the rcu barrier above. We need to + /* This is counterpart of the rcu barriers above. We need to * block potential new user of miniq_old until all readers * are not seeing it. */ -- 2.13.6