On Wed, 20 Dec 2017 16:03:49 -0800, Cong Wang wrote:
> 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;
> }
Looks good after 30 minutes, feel free to add if you post officially:
Tested-by: Jakub Kicinski <jakub.kicin...@netronome.com>
