linux-kernel - [PATCH v2 1/2] PM: s2idle: Drop redundant locks when entering s2idle

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Message-ID: <20250311160827.1129643-2-ulf.hansson@linaro.org>
Date: Tue, 11 Mar 2025 17:08:22 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Rafael J . Wysocki" <rafael@...nel.org>,
	linux-pm@...r.kernel.org
Cc: Len Brown <len.brown@...el.com>,
	Pavel Machek <pavel@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/2] 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@...aro.org>
---

Changes in v2:
 - Added a comment in the code.

---
 kernel/power/suspend.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 09f8397bae15..90fb06ca07d2 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -91,6 +91,8 @@ static void s2idle_enter(void)
 {
 	trace_suspend_resume(TPS("machine_suspend"), PM_SUSPEND_TO_IDLE, true);
 
+	/* CPUs can't be hotplugged here so let's not protect for it. */
+
 	raw_spin_lock_irq(&s2idle_lock);
 	if (pm_wakeup_pending())
 		goto out;
@@ -98,8 +100,6 @@ static void s2idle_enter(void)
 	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 +112,6 @@ static void s2idle_enter(void)
 	 */
 	wake_up_all_idle_cpus();
 
-	cpus_read_unlock();
-
 	raw_spin_lock_irq(&s2idle_lock);
 
  out:
-- 
2.43.0