linux-kernel - Re: [PATCH v9] kernel/fork: beware of __put_task

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Message-ID: <CAAq0SUnNNQr=k8ZJfKsaXgZUCCEFLj6=OCMwRenFCgB9yFKD=g@mail.gmail.com>
Date:   Fri, 9 Jun 2023 16:07:54 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Brian Cain <bcain@...cinc.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Stafford Horne <shorne@...il.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrei Vagin <avagin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...nel.org>,
        Yu Zhao <yuzhao@...gle.com>,
        Alexey Gladkov <legion@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Yang Shi <shy828301@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        Hu Chunyu <chuhu@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Luis Goncalves <lgoncalv@...hat.com>
Subject: Re: [PATCH v9] kernel/fork: beware of __put_task_struct calling context

On Tue, Jun 6, 2023 at 5:40 PM Oleg Nesterov <oleg@...hat.com> wrote:
>
> 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 solve
> the issues with CONFIG_PROVE_RAW_LOCK_NESTING pointed out by Sebastian? Using
> stress-ng or anything else.
>

I managed to test it without a console. No issues happened in the stock kernel.

> This is not that bad, unless I am totally confused the current code (without
> 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() hack
> 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.
>