linux-kernel - [PATCH] cpuidle: menu: Remove incorrect unlikely() annotation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20260105-annotated_idle-v1-1-10ddf0771b58@debian.org>
Date: Mon, 05 Jan 2026 06:37:06 -0800
From: Breno Leitao <leitao@...ian.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>, 
 Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
 kernel-team@...a.com, Breno Leitao <leitao@...ian.org>
Subject: [PATCH] cpuidle: menu: Remove incorrect unlikely() annotation

The unlikely() annotation on the early-return condition in menu_select()
is incorrect on systems with only one idle state (e.g., ARM64 servers
with a single ACPI LPI state). Branch profiling shows 100% misprediction
on such systems since drv->state_count <= 1 is always true.

On platforms where only state0 is available, this path is the common
case, not an unlikely edge case. Remove the misleading annotation to
let the branch predictor learn the actual behavior.

Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 drivers/cpuidle/governors/menu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 64d6f7a1c776..ef9c5a84643e 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -271,7 +271,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 		data->bucket = BUCKETS - 1;
 	}

-	if (unlikely(drv->state_count <= 1 || latency_req == 0) ||
+	if (drv->state_count <= 1 || latency_req == 0 ||
 	    ((data->next_timer_ns < drv->states[1].target_residency_ns ||
 	      latency_req < drv->states[1].exit_latency_ns) &&
 	     !dev->states_usage[0].disable)) {

---
base-commit: 34aa263125b6732375abcb908d73d98169154bb5
change-id: 20260105-annotated_idle-d6b614ecd207

Best regards,
--  
Breno Leitao <leitao@...ian.org>