linux-kernel - [PATCH v2 1/2] cpuidle: Do not return from cpuidle_play

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Message-ID: <3318440.aeNJFYEL58@rjwysocki.net>
Date: Fri, 15 Nov 2024 21:58:31 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>
Cc: LKML <linux-kernel@...r.kernel.org>, x86 Maintainers <x86@...nel.org>,
 Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>,
 "Gautham R. Shenoy" <gautham.shenoy@....com>,
 Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
 Mario Limonciello <mario.limonciello@....com>,
 Linux ACPI <linux-acpi@...r.kernel.org>
Subject:
 [PATCH v2 1/2] cpuidle: Do not return from cpuidle_play_dead() on callback
 failures

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

If the :enter_dead() idle state callback fails for a certain state,
there may be still a shallower state for which it will work.

Because the only caller of cpuidle_play_dead(), native_play_dead(),
falls back to hlt_play_dead() if it returns an error, it should
better try all of the idle states for which :enter_dead() is present
before failing, so change it accordingly.

Also notice that the :enter_dead() state callback is not expected
to return on success (the CPU should be "dead" then), so make
cpuidle_play_dead() ignore its return value.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Reviewed-by: Mario Limonciello <mario.limonciello@....com>
Tested-by: Mario Limonciello <mario.limonciello@....com> # 6.12-rc7
---

v1 -> v2:
   * Make cpuidle_play_dead() never return 0.
   * Add tags from Mario (I have added them because the change of the patch
     should not make a practical difference, but if you want them to be
     dropped, please let me know).

---
 drivers/cpuidle/cpuidle.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/cpuidle/cpuidle.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/cpuidle.c
+++ linux-pm/drivers/cpuidle/cpuidle.c
@@ -69,11 +69,15 @@ int cpuidle_play_dead(void)
 	if (!drv)
 		return -ENODEV;

-	/* Find lowest-power state that supports long-term idle */
-	for (i = drv->state_count - 1; i >= 0; i--)
+	for (i = drv->state_count - 1; i >= 0; i--) {
 		if (drv->states[i].enter_dead)
-			return drv->states[i].enter_dead(dev, i);
+			drv->states[i].enter_dead(dev, i);
+	}

+	/*
+	 * If :enter_dead() is successful, it will never return, so reaching
+	 * here means that all of them failed above or were not present.
+	 */
 	return -ENODEV;
 }