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Date:   Mon, 6 Feb 2023 17:09:27 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Wander Lairson Costa <wander@redhat.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Andy Lutomirski <luto@kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Andrei Vagin <avagin@gmail.com>,
        linux-kernel@vger.kernel.org (open list),
        Hu Chunyu <chuhu@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Paul McKenney <paulmck@kernel.org>
Subject: Re: [PATCH v4] kernel/fork: beware of __put_task_struct calling
 context
Message-Id: <20230206170927.9d5afee653dfa0738983dbfa@linux-foundation.org>
In-Reply-To: <20230206130449.41360-1-wander@redhat.com>
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On Mon,  6 Feb 2023 10:04:47 -0300 Wander Lairson Costa <wander@redhat.com> wrote:

> Under PREEMPT_RT, __put_task_struct() indirectly acquires sleeping
> locks. Therefore, it can't be called from an non-preemptible context.

Well that's regrettable.  Especially if non-preempt kernels don't do
this.

Why does PREEMPT_RT do this and can it be fixed?

If it cannot be fixed then we should have a might_sleep() in
__put_task_struct() for all kernel configurations, along with an
apologetic comment explaining why.