Re: [PATCH net 3/3] net/sched: taprio: dereference oper and admin sched under RCU in taprio_destroy

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Wed, Sep 14, 2022 at 05:34:39PM +0300, Vladimir Oltean wrote:
> -	if (q->oper_sched)
> -		call_rcu(&q->oper_sched->rcu, taprio_free_sched_cb);
> +	rcu_read_lock();
> +
> +	oper = rcu_dereference(q->oper_sched);
> +	admin = rcu_dereference(q->admin_sched);
> +
> +	if (oper)
> +		call_rcu(&oper->rcu, taprio_free_sched_cb);
>  
> -	if (q->admin_sched)
> -		call_rcu(&q->admin_sched->rcu, taprio_free_sched_cb);
> +	if (admin)
> +		call_rcu(&admin->rcu, taprio_free_sched_cb);
> +
> +	rcu_read_unlock();
>  }

I decided to code up this patch at the last minute, since the sparse
warning was bugging me. But after more testing (including with lockdep,
which says absolutely nothing), I notice some RCU stalls after this
patch. It looks like call_rcu() really doesn't like to be called under
rcu_read_lock(). Please discard this patch set from patchwork, I'll
resend when things will work properly.