From: Stephen Hemminger <stephen@networkplumber•org>
To: Cong Wang <xiyou.wangcong@gmail•com>
Cc: netdev@vger•kernel.org, Xiang Mei <xmei5@asu•edu>
Subject: Re: [Patch net v6 1/8] net_sched: Check the return value of qfq_choose_next_agg()
Date: Tue, 30 Dec 2025 09:24:15 -0800 [thread overview]
Message-ID: <20251230092415.077d176c@phoenix.local> (raw)
In-Reply-To: <20251227194135.1111972-2-xiyou.wangcong@gmail.com>
On Sat, 27 Dec 2025 11:41:28 -0800
Cong Wang <xiyou.wangcong@gmail•com> wrote:
> qfq_choose_next_agg() could return NULL so its return value should be
> properly checked unless NULL is acceptable.
>
> There are two cases we need to deal with:
>
> 1) q->in_serv_agg, which is okay with NULL since it is either checked or
> just compared with other pointer without dereferencing. In fact, it
> is even intentionally set to NULL in one of the cases.
>
> 2) in_serv_agg, which is a temporary local variable, which is not okay
> with NULL, since it is dereferenced immediately, hence must be checked.
>
> This fix corrects one of the 2nd cases, and leaving the 1st case as they are.
>
> Although this bug is triggered with the netem duplicate change, the root
> cause is still within qfq qdisc.
>
> Fixes: 462dbc9101ac ("pkt_sched: QFQ Plus: fair-queueing service at DRR cost")
> Reviewed-by: Xiang Mei <xmei5@asu•edu>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail•com>
Looks correct, if you make a new version might want to add a comment.
If you really want to get picky the rest of the code in QFQ compares
with NULL. i.e (in_serv_agg != NULL)
Acked-by: Stephen Hemminger <stephen@networkplumber•org>
next prev parent reply other threads:[~2025-12-30 17:24 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-27 19:41 [Patch net v6 0/8] netem: Fix skb duplication logic and prevent infinite loops Cong Wang
2025-12-27 19:41 ` [Patch net v6 1/8] net_sched: Check the return value of qfq_choose_next_agg() Cong Wang
2025-12-30 17:24 ` Stephen Hemminger [this message]
2025-12-27 19:41 ` [Patch net v6 2/8] Revert "net/sched: Restrict conditions for adding duplicating netems to qdisc tree" Cong Wang
2025-12-27 19:41 ` [Patch net v6 3/8] Revert "selftests/tc-testing: Add tests for restrictions on netem duplication" Cong Wang
2025-12-27 19:41 ` [Patch net v6 4/8] net_sched: Implement the right netem duplication behavior Cong Wang
2025-12-30 17:28 ` Stephen Hemminger
2026-01-04 19:19 ` Jakub Kicinski
2026-01-07 23:33 ` Cong Wang
2026-01-08 2:18 ` Jakub Kicinski
2025-12-27 19:41 ` [Patch net v6 5/8] selftests/tc-testing: Add a nested netem duplicate test Cong Wang
2025-12-27 19:41 ` [Patch net v6 6/8] selftests/tc-testing: Add a test case for piro with netem duplicate Cong Wang
2026-01-04 19:15 ` Jakub Kicinski
2026-01-07 23:34 ` Cong Wang
2025-12-27 19:41 ` [Patch net v6 7/8] selftests/tc-testing: Add a test case for mq " Cong Wang
2025-12-27 19:41 ` [Patch net v6 8/8] selftests/tc-testing: Update test cases " Cong Wang
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