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Date:   Fri, 27 Oct 2023 21:20:26 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Frederic Weisbecker <frederic@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Neeraj Upadhyay <neeraj.upadhyay@amd.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Uladzislau Rezki <urezki@gmail.com>, rcu <rcu@vger.kernel.org>,
        Zqiang <qiang.zhang1211@gmail.com>,
        "Liam R . Howlett" <Liam.Howlett@oracle.com>
Subject: Re: [PATCH 2/4] rcu/tasks: Handle new PF_IDLE semantics
Message-ID: <20231027192026.GG26550@noisy.programming.kicks-ass.net>
References: <20231027144050.110601-1-frederic@kernel.org>
 <20231027144050.110601-3-frederic@kernel.org>
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On Fri, Oct 27, 2023 at 04:40:48PM +0200, Frederic Weisbecker wrote:

> +	/* Has the task been seen voluntarily sleeping? */
> +	if (!READ_ONCE(t->on_rq))
> +		return false;

> -	if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {

AFAICT this ->on_rq usage is outside of scheduler locks and that
READ_ONCE isn't going to help much.

Obviously a pre-existing issue, and I suppose all it cares about is
seeing a 0 or not, irrespective of the races, but urgh..