linux-kernel - Re: [PATCH v2 net 6/6] net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting

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Message-ID: <ZGxD1U4fI8SNSNOW@C02FL77VMD6R.googleapis.com>
Date:   Mon, 22 May 2023 21:40:53 -0700
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Pedro Tammela <pctammela@...atatu.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Peilin Ye <peilin.ye@...edance.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Hillf Danton <hdanton@...a.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        Vlad Buslov <vladbu@...dia.com>
Subject: Re: [PATCH v2 net 6/6] net/sched: qdisc_destroy() old ingress and
 clsact Qdiscs before grafting

Hi Pedro,

On Tue, May 23, 2023 at 12:51:44AM -0300, Pedro Tammela wrote:
> With V2 patches 5 and 6 applied I was still able to trigger an oops.
>
> Branch is 'net' + patches 5 & 6:
> 145f639b9403 (HEAD -> main) net/sched: qdisc_destroy() old ingress and
> clsact Qdiscs before grafting
> 1aac74ef9673 net/sched: Refactor qdisc_graft() for ingress and clsact Qdiscs
> 18c40a1cc1d9 (origin/main, origin/HEAD) net/handshake: Fix sock->file
> allocation
>
> Kernel config is the same as in the syzbot report.
> Note that this was on a _single core_ VM.
> I will double check if v1 is triggering this issue (basically run the repro
> for a long time). For multi-core my VM is running OOM even on a 32Gb system.
> I will check if we have a spare server to run the repro.

Thanks for testing this, but the syzbot reproducer creates ingress Qdiscs
under TC_H_ROOT, which isn't covered by [6/6] i.e. it exercises the
"!ingress" path in qdisc_graft().  I think that's why you are still seeing
the oops.  Adding sch_{ingress,clsact} to TC_H_ROOT is no longer possible
after [1,2/6], and I think we'll need a different reproducer for [5,6/6].

However I just noticed that for some reason my git-send-email in my new
setup didn't auto-generate From: tags with my work email, so Author: will
be my personal email (I have to send patches from personal email to avoid
"[External] " subject prefixes) ... I will fix it in v3 soon.  Sorry in
advance for spamming.

Thanks,
Peilin Ye