sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 100 insertions, 0 deletions

diff --git a/net/bluetooth/leds.c b/net/bluetooth/leds.c
new file mode 100644
index 000000000..6e349704e
--- /dev/null
+++ b/net/bluetooth/leds.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2015, Heiner Kallweit <hkallweit1@gmail.com>
+ */
+
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci_core.h>
+
+#include "leds.h"
+
+DEFINE_LED_TRIGGER(bt_power_led_trigger);
+
+struct hci_basic_led_trigger {
+	struct led_trigger	led_trigger;
+	struct hci_dev		*hdev;
+};
+
+#define to_hci_basic_led_trigger(arg) container_of(arg, \
+			struct hci_basic_led_trigger, led_trigger)
+
+void hci_leds_update_powered(struct hci_dev *hdev, bool enabled)
+{
+	if (hdev->power_led)
+		led_trigger_event(hdev->power_led,
+				  enabled ? LED_FULL : LED_OFF);
+
+	if (!enabled) {
+		struct hci_dev *d;
+
+		read_lock(&hci_dev_list_lock);
+
+		list_for_each_entry(d, &hci_dev_list, list) {
+			if (test_bit(HCI_UP, &d->flags))
+				enabled = true;
+		}
+
+		read_unlock(&hci_dev_list_lock);
+	}
+
+	led_trigger_event(bt_power_led_trigger, enabled ? LED_FULL : LED_OFF);
+}
+
+static int power_activate(struct led_classdev *led_cdev)
+{
+	struct hci_basic_led_trigger *htrig;
+	bool powered;
+
+	htrig = to_hci_basic_led_trigger(led_cdev->trigger);
+	powered = test_bit(HCI_UP, &htrig->hdev->flags);
+
+	led_set_brightness(led_cdev, powered ? LED_FULL : LED_OFF);
+
+	return 0;
+}
+
+static struct led_trigger *led_allocate_basic(struct hci_dev *hdev,
+			int (*activate)(struct led_classdev *led_cdev),
+			const char *name)
+{
+	struct hci_basic_led_trigger *htrig;
+
+	htrig =	devm_kzalloc(&hdev->dev, sizeof(*htrig), GFP_KERNEL);
+	if (!htrig)
+		return NULL;
+
+	htrig->hdev = hdev;
+	htrig->led_trigger.activate = activate;
+	htrig->led_trigger.name = devm_kasprintf(&hdev->dev, GFP_KERNEL,
+						 "%s-%s", hdev->name,
+						 name);
+	if (!htrig->led_trigger.name)
+		goto err_alloc;
+
+	if (devm_led_trigger_register(&hdev->dev, &htrig->led_trigger))
+		goto err_register;
+
+	return &htrig->led_trigger;
+
+err_register:
+	devm_kfree(&hdev->dev, (void *)htrig->led_trigger.name);
+err_alloc:
+	devm_kfree(&hdev->dev, htrig);
+	return NULL;
+}
+
+void hci_leds_init(struct hci_dev *hdev)
+{
+	/* initialize power_led */
+	hdev->power_led = led_allocate_basic(hdev, power_activate, "power");
+}
+
+void bt_leds_init(void)
+{
+	led_trigger_register_simple("bluetooth-power", &bt_power_led_trigger);
+}
+
+void bt_leds_cleanup(void)
+{
+	led_trigger_unregister_simple(bt_power_led_trigger);
+}