Re: [PATCH 2/4] rcu/tasks: Handle new PF_IDLE semantics

[Peter Zijlstra]

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..