From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Aboorva Devarajan <aboorvad@linux.ibm.com>,
	Christian Loehle <christian.loehle@arm.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.19 631/781] cpuidle: Skip governor when only one idle state is available
Date: Tue, 24 Feb 2026 17:22:20 -0800
Message-ID: <20260225012415.286207835@linuxfoundation.org>
In-Reply-To: <20260225012359.695468795@linuxfoundation.org>
References: <20260225012359.695468795@linuxfoundation.org>
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6.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Aboorva Devarajan <aboorvad@linux.ibm.com>

[ Upstream commit e5c9ffc6ae1bcdb1062527d611043681ac301aca ]

On certain platforms (PowerNV systems without a power-mgt DT node),
cpuidle may register only a single idle state. In cases where that
single state is a polling state (state 0), the ladder governor may
incorrectly treat state 1 as the first usable state and pass an
out-of-bounds index. This can lead to a NULL enter callback being
invoked, ultimately resulting in a system crash.

[   13.342636] cpuidle-powernv : Only Snooze is available
[   13.351854] Faulting instruction address: 0x00000000
[   13.376489] NIP [0000000000000000] 0x0
[   13.378351] LR  [c000000001e01974] cpuidle_enter_state+0x2c4/0x668

Fix this by adding a bail-out in cpuidle_select() that returns state 0
directly when state_count <= 1, bypassing the governor and keeping the
tick running.

Fixes: dc2251bf98c6 ("cpuidle: Eliminate the CPUIDLE_DRIVER_STATE_START symbol")
Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260216185005.1131593-2-aboorvad@linux.ibm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/cpuidle/cpuidle.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index c7876e9e024f9..65fbb8e807b97 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -359,6 +359,16 @@ noinstr int cpuidle_enter_state(struct cpuidle_device *dev,
 int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 		   bool *stop_tick)
 {
+	/*
+	 * If there is only a single idle state (or none), there is nothing
+	 * meaningful for the governor to choose. Skip the governor and
+	 * always use state 0 with the tick running.
+	 */
+	if (drv->state_count <= 1) {
+		*stop_tick = false;
+		return 0;
+	}
+
 	return cpuidle_curr_governor->select(drv, dev, stop_tick);
 }
 
-- 
2.51.0