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, 242 insertions, 0 deletions

diff --git a/drivers/input/keyboard/amikbd.c b/drivers/input/keyboard/amikbd.c
new file mode 100644
index 000000000..ecfae0b0b
--- /dev/null
+++ b/drivers/input/keyboard/amikbd.c
@@ -0,0 +1,242 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ *
+ *  Based on the work of:
+ *	Hamish Macdonald
+ */
+
+/*
+ * Amiga keyboard driver for Linux/m68k
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/keyboard.h>
+#include <linux/platform_device.h>
+
+#include <asm/amigaints.h>
+#include <asm/amigahw.h>
+#include <asm/irq.h>
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION("Amiga keyboard driver");
+MODULE_LICENSE("GPL");
+
+#ifdef CONFIG_VT
+static unsigned char amikbd_keycode[0x78] __initdata = {
+	[0]	 = KEY_GRAVE,
+	[1]	 = KEY_1,
+	[2]	 = KEY_2,
+	[3]	 = KEY_3,
+	[4]	 = KEY_4,
+	[5]	 = KEY_5,
+	[6]	 = KEY_6,
+	[7]	 = KEY_7,
+	[8]	 = KEY_8,
+	[9]	 = KEY_9,
+	[10]	 = KEY_0,
+	[11]	 = KEY_MINUS,
+	[12]	 = KEY_EQUAL,
+	[13]	 = KEY_BACKSLASH,
+	[15]	 = KEY_KP0,
+	[16]	 = KEY_Q,
+	[17]	 = KEY_W,
+	[18]	 = KEY_E,
+	[19]	 = KEY_R,
+	[20]	 = KEY_T,
+	[21]	 = KEY_Y,
+	[22]	 = KEY_U,
+	[23]	 = KEY_I,
+	[24]	 = KEY_O,
+	[25]	 = KEY_P,
+	[26]	 = KEY_LEFTBRACE,
+	[27]	 = KEY_RIGHTBRACE,
+	[29]	 = KEY_KP1,
+	[30]	 = KEY_KP2,
+	[31]	 = KEY_KP3,
+	[32]	 = KEY_A,
+	[33]	 = KEY_S,
+	[34]	 = KEY_D,
+	[35]	 = KEY_F,
+	[36]	 = KEY_G,
+	[37]	 = KEY_H,
+	[38]	 = KEY_J,
+	[39]	 = KEY_K,
+	[40]	 = KEY_L,
+	[41]	 = KEY_SEMICOLON,
+	[42]	 = KEY_APOSTROPHE,
+	[43]	 = KEY_BACKSLASH,
+	[45]	 = KEY_KP4,
+	[46]	 = KEY_KP5,
+	[47]	 = KEY_KP6,
+	[48]	 = KEY_102ND,
+	[49]	 = KEY_Z,
+	[50]	 = KEY_X,
+	[51]	 = KEY_C,
+	[52]	 = KEY_V,
+	[53]	 = KEY_B,
+	[54]	 = KEY_N,
+	[55]	 = KEY_M,
+	[56]	 = KEY_COMMA,
+	[57]	 = KEY_DOT,
+	[58]	 = KEY_SLASH,
+	[60]	 = KEY_KPDOT,
+	[61]	 = KEY_KP7,
+	[62]	 = KEY_KP8,
+	[63]	 = KEY_KP9,
+	[64]	 = KEY_SPACE,
+	[65]	 = KEY_BACKSPACE,
+	[66]	 = KEY_TAB,
+	[67]	 = KEY_KPENTER,
+	[68]	 = KEY_ENTER,
+	[69]	 = KEY_ESC,
+	[70]	 = KEY_DELETE,
+	[74]	 = KEY_KPMINUS,
+	[76]	 = KEY_UP,
+	[77]	 = KEY_DOWN,
+	[78]	 = KEY_RIGHT,
+	[79]	 = KEY_LEFT,
+	[80]	 = KEY_F1,
+	[81]	 = KEY_F2,
+	[82]	 = KEY_F3,
+	[83]	 = KEY_F4,
+	[84]	 = KEY_F5,
+	[85]	 = KEY_F6,
+	[86]	 = KEY_F7,
+	[87]	 = KEY_F8,
+	[88]	 = KEY_F9,
+	[89]	 = KEY_F10,
+	[90]	 = KEY_KPLEFTPAREN,
+	[91]	 = KEY_KPRIGHTPAREN,
+	[92]	 = KEY_KPSLASH,
+	[93]	 = KEY_KPASTERISK,
+	[94]	 = KEY_KPPLUS,
+	[95]	 = KEY_HELP,
+	[96]	 = KEY_LEFTSHIFT,
+	[97]	 = KEY_RIGHTSHIFT,
+	[98]	 = KEY_CAPSLOCK,
+	[99]	 = KEY_LEFTCTRL,
+	[100]	 = KEY_LEFTALT,
+	[101]	 = KEY_RIGHTALT,
+	[102]	 = KEY_LEFTMETA,
+	[103]	 = KEY_RIGHTMETA
+};
+
+static void __init amikbd_init_console_keymaps(void)
+{
+	/* We can spare 512 bytes on stack for temp_map in init path. */
+	unsigned short temp_map[NR_KEYS];
+	int i, j;
+
+	for (i = 0; i < MAX_NR_KEYMAPS; i++) {
+		if (!key_maps[i])
+			continue;
+		memset(temp_map, 0, sizeof(temp_map));
+		for (j = 0; j < 0x78; j++) {
+			if (!amikbd_keycode[j])
+				continue;
+			temp_map[j] = key_maps[i][amikbd_keycode[j]];
+		}
+		for (j = 0; j < NR_KEYS; j++) {
+			if (!temp_map[j])
+				temp_map[j] = 0xf200;
+		}
+		memcpy(key_maps[i], temp_map, sizeof(temp_map));
+	}
+}
+#else /* !CONFIG_VT */
+static inline void amikbd_init_console_keymaps(void) {}
+#endif /* !CONFIG_VT */
+
+static const char *amikbd_messages[8] = {
+	[0] = KERN_ALERT "amikbd: Ctrl-Amiga-Amiga reset warning!!\n",
+	[1] = KERN_WARNING "amikbd: keyboard lost sync\n",
+	[2] = KERN_WARNING "amikbd: keyboard buffer overflow\n",
+	[3] = KERN_WARNING "amikbd: keyboard controller failure\n",
+	[4] = KERN_ERR "amikbd: keyboard selftest failure\n",
+	[5] = KERN_INFO "amikbd: initiate power-up key stream\n",
+	[6] = KERN_INFO "amikbd: terminate power-up key stream\n",
+	[7] = KERN_WARNING "amikbd: keyboard interrupt\n"
+};
+
+static irqreturn_t amikbd_interrupt(int irq, void *data)
+{
+	struct input_dev *dev = data;
+	unsigned char scancode, down;
+
+	scancode = ~ciaa.sdr;		/* get and invert scancode (keyboard is active low) */
+	ciaa.cra |= 0x40;		/* switch SP pin to output for handshake */
+	udelay(85);			/* wait until 85 us have expired */
+	ciaa.cra &= ~0x40;		/* switch CIA serial port to input mode */
+
+	down = !(scancode & 1);		/* lowest bit is release bit */
+	scancode >>= 1;
+
+	if (scancode < 0x78) {		/* scancodes < 0x78 are keys */
+		if (scancode == 98) {	/* CapsLock is a toggle switch key on Amiga */
+			input_report_key(dev, scancode, 1);
+			input_report_key(dev, scancode, 0);
+		} else {
+			input_report_key(dev, scancode, down);
+		}
+
+		input_sync(dev);
+	} else				/* scancodes >= 0x78 are error codes */
+		printk(amikbd_messages[scancode - 0x78]);
+
+	return IRQ_HANDLED;
+}
+
+static int __init amikbd_probe(struct platform_device *pdev)
+{
+	struct input_dev *dev;
+	int i, err;
+
+	dev = devm_input_allocate_device(&pdev->dev);
+	if (!dev) {
+		dev_err(&pdev->dev, "Not enough memory for input device\n");
+		return -ENOMEM;
+	}
+
+	dev->name = pdev->name;
+	dev->phys = "amikbd/input0";
+	dev->id.bustype = BUS_AMIGA;
+	dev->id.vendor = 0x0001;
+	dev->id.product = 0x0001;
+	dev->id.version = 0x0100;
+
+	dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REP);
+
+	for (i = 0; i < 0x78; i++)
+		set_bit(i, dev->keybit);
+
+	amikbd_init_console_keymaps();
+
+	ciaa.cra &= ~0x41;	 /* serial data in, turn off TA */
+	err = devm_request_irq(&pdev->dev, IRQ_AMIGA_CIAA_SP, amikbd_interrupt,
+			       0, "amikbd", dev);
+	if (err)
+		return err;
+
+	err = input_register_device(dev);
+	if (err)
+		return err;
+
+	platform_set_drvdata(pdev, dev);
+
+	return 0;
+}
+
+static struct platform_driver amikbd_driver = {
+	.driver   = {
+		.name	= "amiga-keyboard",
+	},
+};
+
+module_platform_driver_probe(amikbd_driver, amikbd_probe);
+
+MODULE_ALIAS("platform:amiga-keyboard");