Re: [PATCH v2 net 6/7] net/sched: taprio: fix q->current_entry is NULL before its expiry

[Abdul Rahim, Faizal]

On 9/11/2023 7:55 pm, Vladimir Oltean wrote:
> On Tue, Nov 07, 2023 at 06:20:22AM -0500, Faizal Rahim wrote:
> > Fix the issue of prematurely setting q->current_entry to NULL in the
> > setup_first_end_time() function when a new admin schedule arrives
> > while the oper schedule is still running but hasn't transitioned yet.
> > This premature setting causes problems because any reference to
> > q->current_entry, such as in taprio_dequeue(), will result in NULL
> > during this period, which is incorrect. q->current_entry should remain
> > valid until the currently running entry expires.
> >
> > To address this issue, only set q->current_entry to NULL when there is
> > no oper schedule currently running.
> >
> > Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler")
>
> The "Fixes" tag represents the commit where the code started becoming a
> problem, not when the code that you're changing was first introduced.
>
> I find it hard to believe that the problem was in commit 5a781ccbd19e
> ("tc: Add support for configuring the taprio scheduler"), because we
> didn't support admin -> oper dynamic schedules back then.

My bad, will update accordingly.

> > Signed-off-by: Faizal Rahim <faizal.abdul.rahim@xxxxxxxxxxxxxxx>
> > ---
> >   net/sched/sch_taprio.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> > index 01b114edec30..c60e9e7ac193 100644
> > --- a/net/sched/sch_taprio.c
> > +++ b/net/sched/sch_taprio.c
> > @@ -1375,7 +1375,8 @@ static void setup_first_end_time(struct taprio_sched *q,
> >   			first->gate_close_time[tc] = ktime_add_ns(base, first->gate_duration[tc]);
> >   	}
> >   
> > -	rcu_assign_pointer(q->current_entry, NULL);
> > +	if (!hrtimer_active(&q->advance_timer))
> > +		rcu_assign_pointer(q->current_entry, NULL);
> >   }
> >   
> >   static void taprio_start_sched(struct Qdisc *sch,
> > --
> > 2.25.1