netdev - Re: [PATCH net] sch_htb: Avoid grafting on htb_destroy_class

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Date:   Wed, 11 Jan 2023 10:13:06 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Rahul Rameshbabu <rrameshbabu@...dia.com>
Cc:     netdev@...r.kernel.org, Tariq Toukan <tariqt@...dia.com>,
        Gal Pressman <gal@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Maxim Mikityanskiy <maxtram95@...il.com>
Subject: Re: [PATCH net] sch_htb: Avoid grafting on htb_destroy_class_offload
 when destroying htb

Tue, Jan 10, 2023 at 09:20:04PM CET, rrameshbabu@...dia.com wrote:
>Peek at old qdisc and graft only when deleting leaf class in the htb. When
>destroying the htb, the caller may already have grafted a new qdisc that is
>not part of the htb structure being destroyed. htb_destroy_class_offload
>should not peek at the qdisc of the netdev queue since that will either be

You are not telling the codebase what to do. Do it in order to make it
obvious what the patch is doing. That makes the patch description easier
to understand.


>the new qdisc in the case of replacing the htb or simply a noop_qdisc is
>the case of destroying the htb without a replacement qdisc.


Looks to me like 2 fixes, shouldn't this be 2 patches instead?


>
>Fixes: d03b195b5aa0 ("sch_htb: Hierarchical QoS hardware offload")
>Signed-off-by: Rahul Rameshbabu <rrameshbabu@...dia.com>
>Cc: Eric Dumazet <edumazet@...gle.com>
>Cc: Maxim Mikityanskiy <maxtram95@...il.com>
>---
> net/sched/sch_htb.c | 23 +++++++++++++----------
> 1 file changed, 13 insertions(+), 10 deletions(-)
>
>diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
>index 2238edece1a4..360ce8616fd2 100644
>--- a/net/sched/sch_htb.c
>+++ b/net/sched/sch_htb.c
>@@ -1557,14 +1557,13 @@ static int htb_destroy_class_offload(struct Qdisc *sch, struct htb_class *cl,
> 
> 	WARN_ON(!q);
> 	dev_queue = htb_offload_get_queue(cl);
>-	old = htb_graft_helper(dev_queue, NULL);
>-	if (destroying)
>-		/* Before HTB is destroyed, the kernel grafts noop_qdisc to
>-		 * all queues.
>+	if (!destroying) {
>+		old = htb_graft_helper(dev_queue, NULL);
>+		/* Last qdisc grafted should be the same as cl->leaf.q when
>+		 * calling htb_destroy
> 		 */
>-		WARN_ON(!(old->flags & TCQ_F_BUILTIN));
>-	else
> 		WARN_ON(old != q);
>+	}
> 
> 	if (cl->parent) {
> 		_bstats_update(&cl->parent->bstats_bias,
>@@ -1581,10 +1580,14 @@ static int htb_destroy_class_offload(struct Qdisc *sch, struct htb_class *cl,
> 	};
> 	err = htb_offload(qdisc_dev(sch), &offload_opt);
> 
>-	if (!err || destroying)
>-		qdisc_put(old);
>-	else
>-		htb_graft_helper(dev_queue, old);
>+	/* htb_offload related errors when destroying cannot be handled */
>+	WARN_ON(err && destroying);
>+	if (!destroying) {
>+		if (!err)
>+			qdisc_put(old);
>+		else
>+			htb_graft_helper(dev_queue, old);
>+	}
> 
> 	if (last_child)
> 		return err;
>-- 
>2.36.2
>