[PATCH 5.15 155/164] cpuidle: Skip governor when only one idle state is available

Sasha Levin
2026-02-28T18:17:15Z

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 e371d6972f8d9..20b9f77a8fb02 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -319,6 +319,16 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
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