netdev - Re: [PATCH net v2 0/5] net_sched: Adapt qdiscs for reentrant enqueue cases

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Message-ID: <aAl34pi75s8ItSme@pop-os.localdomain>
Date: Wed, 23 Apr 2025 16:29:38 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Victor Nogueira <victor@...atatu.com>, netdev@...r.kernel.org,
	jhs@...atatu.com, jiri@...nulli.us, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, toke@...hat.com,
	gerrard.tai@...rlabs.sg, pctammela@...atatu.com
Subject: Re: [PATCH net v2 0/5] net_sched: Adapt qdiscs for reentrant enqueue
 cases

On Wed, Apr 23, 2025 at 01:50:50PM -0700, Cong Wang wrote:
> diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> index fdd79d3ccd8c..000f8138f561 100644
> --- a/net/sched/sch_netem.c
> +++ b/net/sched/sch_netem.c
> @@ -531,21 +531,6 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
>  		return NET_XMIT_DROP;
>  	}
>  
> -	/*
> -	 * If doing duplication then re-insert at top of the
> -	 * qdisc tree, since parent queuer expects that only one
> -	 * skb will be queued.
> -	 */
> -	if (skb2) {
> -		struct Qdisc *rootq = qdisc_root_bh(sch);
> -		u32 dupsave = q->duplicate; /* prevent duplicating a dup... */
> -
> -		q->duplicate = 0;
> -		rootq->enqueue(skb2, rootq, to_free);
> -		q->duplicate = dupsave;
> -		skb2 = NULL;
> -	}
> -
>  	qdisc_qstats_backlog_inc(sch, skb);
>  
>  	cb = netem_skb_cb(skb);
> @@ -613,6 +598,21 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
>  		sch->qstats.requeues++;
>  	}
>  
> +	/*
> +	 * If doing duplication then re-insert at top of the
> +	 * qdisc tree, since parent queuer expects that only one
> +	 * skb will be queued.
> +	 */
> +	if (skb2) {
> +		struct Qdisc *rootq = qdisc_root_bh(sch);
> +		u32 dupsave = q->duplicate; /* prevent duplicating a dup... */
> +
> +		q->duplicate = 0;
> +		rootq->enqueue(skb2, rootq, to_free);
> +		q->duplicate = dupsave;
> +		skb2 = NULL;
> +	}
> +
>  finish_segs:
>  	if (skb2)
>  		__qdisc_drop(skb2, to_free);
> 

Just FYI: I tested this patch, netem duplication still worked, I didn't
see any issue.

Thanks.