Subject: Re: [PATCH] pkt_sched: Fix qdisc_watchdog() vs. dev_deactivate() race

From: Jarek Poplawski <[email-masked]>
Date: Thu, 21 Aug 2008 05:17:37 +0000

On Wed, Aug 20, 2008 at 11:56:56AM +0000, Jarek Poplawski wrote:
...
> pkt_sched: Fix qdisc_watchdog() vs. dev_deactivate() race
> 
> dev_deactivate() can skip rescheduling of a qdisc by qdisc_watchdog()
> or other timer calling netif_schedule() after dev_queue_deactivate().
> We prevent this checking aliveness before scheduling the timer.
> 
> With feedback from Herbert Xu <[email-masked]>
> 
> Signed-off-by: Jarek Poplawski <[email-masked]>
> 

Actually, this patch is "no good" (wrong root qdisc).

David, please don't apply - I'll send it redone.

Thanks,
Jarek P.

> ---
> 
>  net/sched/sch_api.c |    3 +++
>  net/sched/sch_cbq.c |    3 +++
>  2 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index ef0efec..6f2bc7f 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -444,6 +444,9 @@ void qdisc_watchdog_schedule(struct qdisc_watchdog *wd, psched_time_t expires)
>  {
>  	ktime_t time;
>  
> +	if (test_bit(__QDISC_STATE_DEACTIVATED, &qdisc_root(wd->qdisc)->state))
> +		return;
> +
>  	wd->qdisc->flags |= TCQ_F_THROTTLED;
>  	time = ktime_set(0, 0);
>  	time = ktime_add_ns(time, PSCHED_US2NS(expires));
> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> index 47ef492..c04d335 100644
> --- a/net/sched/sch_cbq.c
> +++ b/net/sched/sch_cbq.c
> @@ -521,6 +521,9 @@ static void cbq_ovl_delay(struct cbq_class *cl)
>  	struct cbq_sched_data *q = qdisc_priv(cl->qdisc);
>  	psched_tdiff_t delay = cl->undertime - q->now;
>  
> +	if (test_bit(__QDISC_STATE_DEACTIVATED, &qdisc_root(cl->qdisc)->state))
> +		return;
> +
>  	if (!cl->delayed) {
>  		psched_time_t sched = q->now;
>  		ktime_t expires;