netdev - Re: [net-next PATCH 05/15] net: sched: a dflt qdisc may be used with per cpu stats

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Message-ID: <1472056898.14381.95.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 24 Aug 2016 09:41:38 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     jhs@...atatu.com, davem@...emloft.net, brouer@...hat.com,
        xiyou.wangcong@...il.com, alexei.starovoitov@...il.com,
        john.r.fastabend@...el.com, netdev@...r.kernel.org
Subject: Re: [net-next PATCH 05/15] net: sched: a dflt qdisc may be used
 with per cpu stats

On Tue, 2016-08-23 at 13:24 -0700, John Fastabend wrote:
> Enable dflt qdisc support for per cpu stats before this patch a
> dflt qdisc was required to use the global statistics qstats and
> bstats.
> 
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> ---
>  net/sched/sch_generic.c |   24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
> index 80544c2..910b4d15 100644
> --- a/net/sched/sch_generic.c
> +++ b/net/sched/sch_generic.c
> @@ -646,18 +646,34 @@ struct Qdisc *qdisc_create_dflt(struct netdev_queue *dev_queue,
>  	struct Qdisc *sch;
>  
>  	if (!try_module_get(ops->owner))
> -		goto errout;
> +		return NULL;
>  
>  	sch = qdisc_alloc(dev_queue, ops);
>  	if (IS_ERR(sch))
> -		goto errout;
> +		return NULL;
>  	sch->parent = parentid;
>  
> -	if (!ops->init || ops->init(sch, NULL) == 0)
> +	if (!ops->init)
>  		return sch;
>  
> -	qdisc_destroy(sch);
> +	if (ops->init(sch, NULL))
> +		goto errout;
> +
> +	/* init() may have set percpu flags so init data structures */
> +	if (qdisc_is_percpu_stats(sch)) {
> +		sch->cpu_bstats =
> +			netdev_alloc_pcpu_stats(struct gnet_stats_basic_cpu);
> +		if (!sch->cpu_bstats)
> +			goto errout;
> +
> +		sch->cpu_qstats = alloc_percpu(struct gnet_stats_queue);
> +		if (!sch->cpu_qstats)
> +			goto errout;
> +	}
> +

Why are you attempting these allocations here instead of qdisc_alloc()

This looks weird, I would expect base qdisc being fully allocated before
ops->init() is attempted.