On Wed, Dec 20, 2017 at 10:31 AM, Cong Wang <xiyou.wangc...@gmail.com> wrote:
> On Wed, Dec 20, 2017 at 10:17 AM, Cong Wang <xiyou.wangc...@gmail.com> wrote:
>>
>> I guess it is q->miniqp which is freed in qdisc_graft() without properly
>> waiting for rcu readers?
>
> It is probably so, the call_rcu_bh(&miniq_old->rcu, mini_qdisc_rcu_func)
> in the end of mini_qdisc_pair_swap() is invoked on miniq_old->rcu,
> but miniq is being freed, no rcu barrier waits for it...
>
> You can try to add a rcu_barrier_bh() at the end to see if this crash
> is gone, but I don't think people like adding yet another rcu barrier...
Hi, Jakub
Can you test the following fix? I am not a fan of rcu barrier but we
already have one so...
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 876fab2604b8..1b68fedea124 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1240,6 +1240,8 @@ void mini_qdisc_pair_swap(struct mini_Qdisc_pair *miniqp,
if (!tp_head) {
RCU_INIT_POINTER(*miniqp->p_miniq, NULL);
+ /* Wait for existing flying RCU callback before being freed. */
+ rcu_barrier_bh();
return;
}
