sched/smp: Use the SMP version of __task_needs_rq_lock()

Simplify the scheduler by making CONFIG_SMP=y code in
__task_needs_rq_lock() unconditional.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20250528080924.2273858-25-mingo@kernel.org

kernel/sched/core.c

@@ -4312,14 +4312,12 @@ static bool __task_needs_rq_lock(struct task_struct *p)
 	if (p->on_rq)
 		return true;
 
-#ifdef CONFIG_SMP
 	/*
 	 * Ensure the task has finished __schedule() and will not be referenced
 	 * anymore. Again, see try_to_wake_up() for a longer comment.
 	 */
 	smp_rmb();
 	smp_cond_load_acquire(&p->on_cpu, !VAL);
-#endif
 
 	return false;
 }