linux-kernel - [RFC PATCH v4 1/8] cpuidle: Do not return from cpuidle_play

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Message-ID: <20241125132029.7241-2-patryk.wlazlyn@linux.intel.com>
Date: Mon, 25 Nov 2024 14:20:21 +0100
From: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	rafael.j.wysocki@...el.com,
	len.brown@...el.com,
	artem.bityutskiy@...ux.intel.com,
	dave.hansen@...ux.intel.com,
	patryk.wlazlyn@...ux.intel.com,
	peterz@...radead.org,
	tglx@...utronix.de,
	gautham.shenoy@....com
Subject: [RFC PATCH v4 1/8] 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
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>
---
 drivers/cpuidle/cpuidle.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 06ace16f9e71..0835da449db8 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/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;
 }
 
-- 
2.47.0