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, 232 insertions, 0 deletions

diff --git a/drivers/input/keyboard/atakbd.c b/drivers/input/keyboard/atakbd.c
new file mode 100644
index 000000000..07e17e563
--- /dev/null
+++ b/drivers/input/keyboard/atakbd.c
@@ -0,0 +1,232 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  atakbd.c
+ *
+ *  Copyright (c) 2005 Michael Schmitz
+ *
+ * Based on amikbd.c, which is
+ *
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ *
+ *  Based on the work of:
+ *	Hamish Macdonald
+ */
+
+/*
+ * Atari keyboard driver for Linux/m68k
+ *
+ * The low level init and interrupt stuff is handled in arch/mm68k/atari/atakeyb.c
+ * (the keyboard ACIA also handles the mouse and joystick data, and the keyboard
+ * interrupt is shared with the MIDI ACIA so MIDI data also get handled there).
+ * This driver only deals with handing key events off to the input layer.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+
+#include <asm/atariints.h>
+#include <asm/atarihw.h>
+#include <asm/atarikb.h>
+#include <asm/irq.h>
+
+MODULE_AUTHOR("Michael Schmitz <schmitz@biophys.uni-duesseldorf.de>");
+MODULE_DESCRIPTION("Atari keyboard driver");
+MODULE_LICENSE("GPL");
+
+/*
+ 0x47: KP_7     71
+ 0x48: KP_8     72
+ 0x49: KP_9     73
+ 0x62: KP_/     98
+ 0x4b: KP_4     75
+ 0x4c: KP_5     76
+ 0x4d: KP_6     77
+ 0x37: KP_*     55
+ 0x4f: KP_1     79
+ 0x50: KP_2     80
+ 0x51: KP_3     81
+ 0x4a: KP_-     74
+ 0x52: KP_0     82
+ 0x53: KP_.     83
+ 0x4e: KP_+     78
+
+ 0x67: Up       103
+ 0x6c: Down     108
+ 0x69: Left     105
+ 0x6a: Right    106
+ */
+
+
+static unsigned char atakbd_keycode[0x73] = {	/* American layout */
+	[1]	 = KEY_ESC,
+	[2]	 = KEY_1,
+	[3]	 = KEY_2,
+	[4]	 = KEY_3,
+	[5]	 = KEY_4,
+	[6]	 = KEY_5,
+	[7]	 = KEY_6,
+	[8]	 = KEY_7,
+	[9]	 = KEY_8,
+	[10]	 = KEY_9,
+	[11]	 = KEY_0,
+	[12]	 = KEY_MINUS,
+	[13]	 = KEY_EQUAL,
+	[14]	 = KEY_BACKSPACE,
+	[15]	 = KEY_TAB,
+	[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,
+	[28]	 = KEY_ENTER,
+	[29]	 = KEY_LEFTCTRL,
+	[30]	 = KEY_A,
+	[31]	 = KEY_S,
+	[32]	 = KEY_D,
+	[33]	 = KEY_F,
+	[34]	 = KEY_G,
+	[35]	 = KEY_H,
+	[36]	 = KEY_J,
+	[37]	 = KEY_K,
+	[38]	 = KEY_L,
+	[39]	 = KEY_SEMICOLON,
+	[40]	 = KEY_APOSTROPHE,
+	[41]	 = KEY_GRAVE,
+	[42]	 = KEY_LEFTSHIFT,
+	[43]	 = KEY_BACKSLASH,
+	[44]	 = KEY_Z,
+	[45]	 = KEY_X,
+	[46]	 = KEY_C,
+	[47]	 = KEY_V,
+	[48]	 = KEY_B,
+	[49]	 = KEY_N,
+	[50]	 = KEY_M,
+	[51]	 = KEY_COMMA,
+	[52]	 = KEY_DOT,
+	[53]	 = KEY_SLASH,
+	[54]	 = KEY_RIGHTSHIFT,
+	[55]	 = KEY_KPASTERISK,
+	[56]	 = KEY_LEFTALT,
+	[57]	 = KEY_SPACE,
+	[58]	 = KEY_CAPSLOCK,
+	[59]	 = KEY_F1,
+	[60]	 = KEY_F2,
+	[61]	 = KEY_F3,
+	[62]	 = KEY_F4,
+	[63]	 = KEY_F5,
+	[64]	 = KEY_F6,
+	[65]	 = KEY_F7,
+	[66]	 = KEY_F8,
+	[67]	 = KEY_F9,
+	[68]	 = KEY_F10,
+	[71]	 = KEY_HOME,
+	[72]	 = KEY_UP,
+	[74]	 = KEY_KPMINUS,
+	[75]	 = KEY_LEFT,
+	[77]	 = KEY_RIGHT,
+	[78]	 = KEY_KPPLUS,
+	[80]	 = KEY_DOWN,
+	[82]	 = KEY_INSERT,
+	[83]	 = KEY_DELETE,
+	[96]	 = KEY_102ND,
+	[97]	 = KEY_UNDO,
+	[98]	 = KEY_HELP,
+	[99]	 = KEY_KPLEFTPAREN,
+	[100]	 = KEY_KPRIGHTPAREN,
+	[101]	 = KEY_KPSLASH,
+	[102]	 = KEY_KPASTERISK,
+	[103]	 = KEY_KP7,
+	[104]	 = KEY_KP8,
+	[105]	 = KEY_KP9,
+	[106]	 = KEY_KP4,
+	[107]	 = KEY_KP5,
+	[108]	 = KEY_KP6,
+	[109]	 = KEY_KP1,
+	[110]	 = KEY_KP2,
+	[111]	 = KEY_KP3,
+	[112]	 = KEY_KP0,
+	[113]	 = KEY_KPDOT,
+	[114]	 = KEY_KPENTER,
+};
+
+static struct input_dev *atakbd_dev;
+
+static void atakbd_interrupt(unsigned char scancode, char down)
+{
+
+	if (scancode < 0x73) {		/* scancodes < 0xf3 are keys */
+
+		// report raw events here?
+
+		scancode = atakbd_keycode[scancode];
+
+		input_report_key(atakbd_dev, scancode, down);
+		input_sync(atakbd_dev);
+	} else				/* scancodes >= 0xf3 are mouse data, most likely */
+		printk(KERN_INFO "atakbd: unhandled scancode %x\n", scancode);
+
+	return;
+}
+
+static int __init atakbd_init(void)
+{
+	int i, error;
+
+	if (!MACH_IS_ATARI || !ATARIHW_PRESENT(ST_MFP))
+		return -ENODEV;
+
+	// need to init core driver if not already done so
+	error = atari_keyb_init();
+	if (error)
+		return error;
+
+	atakbd_dev = input_allocate_device();
+	if (!atakbd_dev)
+		return -ENOMEM;
+
+	atakbd_dev->name = "Atari Keyboard";
+	atakbd_dev->phys = "atakbd/input0";
+	atakbd_dev->id.bustype = BUS_HOST;
+	atakbd_dev->id.vendor = 0x0001;
+	atakbd_dev->id.product = 0x0001;
+	atakbd_dev->id.version = 0x0100;
+
+	atakbd_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REP);
+	atakbd_dev->keycode = atakbd_keycode;
+	atakbd_dev->keycodesize = sizeof(unsigned char);
+	atakbd_dev->keycodemax = ARRAY_SIZE(atakbd_keycode);
+
+	for (i = 1; i < 0x72; i++) {
+		set_bit(atakbd_keycode[i], atakbd_dev->keybit);
+	}
+
+	/* error check */
+	error = input_register_device(atakbd_dev);
+	if (error) {
+		input_free_device(atakbd_dev);
+		return error;
+	}
+
+	atari_input_keyboard_interrupt_hook = atakbd_interrupt;
+
+	return 0;
+}
+
+static void __exit atakbd_exit(void)
+{
+	atari_input_keyboard_interrupt_hook = NULL;
+	input_unregister_device(atakbd_dev);
+}
+
+module_init(atakbd_init);
+module_exit(atakbd_exit);