netdev - Re: [PATCH v3] net/sched: sch_qfq: Fix race condition on qfq

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Message-ID: <aHbTPUYbroQ6W_1j@xps>
Date: Tue, 15 Jul 2025 15:16:29 -0700
From: Xiang Mei <xmei5@....edu>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
	gregkh@...uxfoundation.org, jhs@...atatu.com, jiri@...nulli.us,
	security@...nel.org
Subject: Re: [PATCH v3] net/sched: sch_qfq: Fix race condition on
 qfq_aggregate

On Tue, Jul 15, 2025 at 11:13:23AM -0700, Cong Wang wrote:
> On Mon, Jul 14, 2025 at 05:09:42PM -0700, Xiang Mei wrote:
> > 
> > Here is more information no how I tested:
> > 
> > 1) I ran `python3 ./tdc.py -f ./tc-tests/infra/qdiscs.json -e 5e6d` 100
> > times
> > 2) The KASAN is enabled, and my patch is on it
> > 3) All 100 results show `ok 1 5e6d - Test QFQ's enqueue reentrant behaviour
> > with netem` without any crashing in dmesg
> > 
> > I may need more information to trace this crash.
> 
> Now I figured out why... It is all because of I used a wrong vmlinux to
> test this. Although I switched to vanilla -net branch, I forgot to
> rebuild the vmlinux which was still the one with my netem patches. And I
> just saw "netem duplicate 100%" in test case 5e6d, now it explains
> everything.
> 
> Appologize for my stupid mistake here. I think it is clearly caused by
> my netem duplication patch (although the fix is not necessarily there).
> 
> I will take care of this in my netem patchset.
> 
> Sorry for the noise.

No worries, thanks for the explanations.