netdev - Re: [Patch net v5 5/9] net_sched: Check the return value of qfq_choose_next

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Message-ID: <278eb8cc-0564-4883-918e-0aaa62dfa851@redhat.com>
Date: Tue, 2 Dec 2025 10:20:20 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc: stephen@...workplumber.org, kuba@...nel.org, Xiang Mei <xmei5@....edu>
Subject: Re: [Patch net v5 5/9] net_sched: Check the return value of
 qfq_choose_next_agg()

On 11/26/25 8:52 PM, Cong Wang 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.

Given the above, I think this patch should come first in the series WRT
"net_sched: Implement the right netem duplication behavior"

/P