PM: s2idle: Drop redundant locks when entering s2idle

The calls to cpus_read_lock|unlock() protects us from getting CPUS
hotplugged, while entering suspend-to-idle. However, when s2idle_enter() is
called we should be far beyond the point when CPUs may be hotplugged.
Let's therefore simplify the code and drop the use of the lock.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://patch.msgid.link/20250311160827.1129643-2-ulf.hansson@linaro.org
[ rjw: Rewrote the new comment ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: storulf

kernel/power/suspend.c

@@ -91,15 +91,19 @@ static void s2idle_enter(void)
 {
 	trace_suspend_resume(TPS("machine_suspend"), PM_SUSPEND_TO_IDLE, true);
 
+	/*
+	 * The correctness of the code below depends on the number of online
+	 * CPUs being stable, but CPUs cannot be taken offline or put online
+	 * while it is running.
+	 */
+
 	raw_spin_lock_irq(&s2idle_lock);
 	if (pm_wakeup_pending())
 		goto out;
 
 	s2idle_state = S2IDLE_STATE_ENTER;
 	raw_spin_unlock_irq(&s2idle_lock);
 
-	cpus_read_lock();
-
 	/* Push all the CPUs into the idle loop. */
 	wake_up_all_idle_cpus();
 	/* Make the current CPU wait so it can enter the idle loop too. */
@@ -112,8 +116,6 @@ static void s2idle_enter(void)
 	 */
 	wake_up_all_idle_cpus();
 
-	cpus_read_unlock();
-
 	raw_spin_lock_irq(&s2idle_lock);
 
  out: