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Date: Tue, 21 Apr 2026 14:15:00 +0100
From: Simon Horman <horms@kernel.org>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: netdev@vger.kernel.org, jiri@resnulli.us, jhs@mojatatu.com,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Martin Ottens <martin.ottens@fau.de>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net v8 2/6] net/sched: netem: fix queue limit check to
 include reordered packets
Message-ID: <20260421131500.GB651125@horms.kernel.org>
References: <20260418032027.900913-1-stephen@networkplumber.org>
 <20260418032027.900913-3-stephen@networkplumber.org>
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In-Reply-To: <20260418032027.900913-3-stephen@networkplumber.org>

On Fri, Apr 17, 2026 at 08:19:40PM -0700, Stephen Hemminger wrote:
> The queue limit check in netem_enqueue() uses q->t_len which only
> counts packets in the internal tfifo. Packets placed in sch->q by
> the reorder path (__qdisc_enqueue_head) are not counted, allowing
> the total queue occupancy to exceed sch->limit under reordering.
> 
> Include sch->q.qlen in the limit check.
> 
> Fixes: f8d4bc455047 ("net/sched: netem: account for backlog updates from child qdisc")
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> Reviewed-by: Simon Horman <horms@kernel.org>

I acknowledge that Sashiko has provided review of this patch.

In the case of the commentary on the use of sch->q.qlen in place of q->t_len:
this is exactly the intention of this patch; to address shortcomings
in commit f8d4bc455047. Follow-up issues can be treated as such.

In the case of feedback on us of qdisc_drop_all(): if this is a problem
then it predates this patch and can be addressed separately to this
patch-set.

...