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From:   Wander Lairson Costa <wander@redhat.com>
Date:   Fri, 9 Jun 2023 16:07:54 -0300
Message-ID: <CAAq0SUnNNQr=k8ZJfKsaXgZUCCEFLj6=OCMwRenFCgB9yFKD=g@mail.gmail.com>
Subject: Re: [PATCH v9] kernel/fork: beware of __put_task_struct calling context
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
        Brian Cain <bcain@quicinc.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Stafford Horne <shorne@gmail.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Liam R. Howlett" <Liam.Howlett@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Andrei Vagin <avagin@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Daniel Bristot de Oliveira <bristot@kernel.org>,
        Yu Zhao <yuzhao@google.com>,
        Alexey Gladkov <legion@kernel.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Yang Shi <shy828301@gmail.com>,
        open list <linux-kernel@vger.kernel.org>,
        Hu Chunyu <chuhu@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Luis Goncalves <lgoncalv@redhat.com>
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On Tue, Jun 6, 2023 at 5:40=E2=80=AFPM Oleg Nesterov <oleg@redhat.com> wrot=
e:
>
> On 06/05, Wander Lairson Costa wrote:
> >
> > Thanks. I found an unrelated earlier splat in the console code. That's
> > why I couldn't reproduce it in the stock kernel.
>
> As expected...
>
> So... Not sure what can I say ;) can you verify that this patch doesn't s=
olve
> the issues with CONFIG_PROVE_RAW_LOCK_NESTING pointed out by Sebastian? U=
sing
> stress-ng or anything else.
>

I managed to test it without a console. No issues happened in the stock ker=
nel.

> This is not that bad, unless I am totally confused the current code (with=
out
> your patch) has the same problem (otherwise we wouldn't need this fix).
>

That's my understanding as well.

> But perhaps you can make 2/2 which adds the DEFINE_WAIT_OVERRIDE_MAP() ha=
ck
> as Peter suggested?
>

Yes, sure. I would like to get the issue reproduced in practice to
make sure I am really fixing the problem. But I can live with that.

> Oleg.
>