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

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Message-ID: <aS/N0s3A4xeJqMvZ@pop-os.localdomain>
Date: Tue, 2 Dec 2025 21:42:42 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, 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 Tue, Dec 02, 2025 at 10:20:20AM +0100, Paolo Abeni wrote:
> 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"

Will do.

Regards,
Cong