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, 153 insertions, 0 deletions

diff --git a/drivers/input/mouse/atarimouse.c b/drivers/input/mouse/atarimouse.c
new file mode 100644
index 000000000..b1219cc4d
--- /dev/null
+++ b/drivers/input/mouse/atarimouse.c
@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Atari mouse driver for Linux/m68k
+ *
+ *  Copyright (c) 2005 Michael Schmitz
+ *
+ *  Based on:
+ *  Amiga mouse driver for Linux/m68k
+ *
+ *  Copyright (c) 2000-2002 Vojtech Pavlik
+ */
+/*
+ * 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.
+ *
+ * Largely based on the old:
+ *
+ * Atari Mouse Driver for Linux
+ * by Robert de Vries (robert@and.nl) 19Jul93
+ *
+ * 16 Nov 1994 Andreas Schwab
+ * Compatibility with busmouse
+ * Support for three button mouse (shamelessly stolen from MiNT)
+ * third button wired to one of the joystick directions on joystick 1
+ *
+ * 1996/02/11 Andreas Schwab
+ * Module support
+ * Allow multiple open's
+ *
+ * Converted to use new generic busmouse code.  5 Apr 1998
+ *   Russell King <rmk@arm.uk.linux.org>
+ */
+
+
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+
+#include <asm/irq.h>
+#include <asm/setup.h>
+#include <linux/uaccess.h>
+#include <asm/atarihw.h>
+#include <asm/atarikb.h>
+#include <asm/atariints.h>
+
+MODULE_AUTHOR("Michael Schmitz <schmitz@biophys.uni-duesseldorf.de>");
+MODULE_DESCRIPTION("Atari mouse driver");
+MODULE_LICENSE("GPL");
+
+static int mouse_threshold[2] = {2, 2};
+module_param_array(mouse_threshold, int, NULL, 0);
+
+#ifdef FIXED_ATARI_JOYSTICK
+extern int atari_mouse_buttons;
+#endif
+
+static struct input_dev *atamouse_dev;
+
+static void atamouse_interrupt(char *buf)
+{
+	int buttons, dx, dy;
+
+	buttons = (buf[0] & 1) | ((buf[0] & 2) << 1);
+#ifdef FIXED_ATARI_JOYSTICK
+	buttons |= atari_mouse_buttons & 2;
+	atari_mouse_buttons = buttons;
+#endif
+
+	/* only relative events get here */
+	dx = buf[1];
+	dy = buf[2];
+
+	input_report_rel(atamouse_dev, REL_X, dx);
+	input_report_rel(atamouse_dev, REL_Y, dy);
+
+	input_report_key(atamouse_dev, BTN_LEFT,   buttons & 0x4);
+	input_report_key(atamouse_dev, BTN_MIDDLE, buttons & 0x2);
+	input_report_key(atamouse_dev, BTN_RIGHT,  buttons & 0x1);
+
+	input_sync(atamouse_dev);
+
+	return;
+}
+
+static int atamouse_open(struct input_dev *dev)
+{
+#ifdef FIXED_ATARI_JOYSTICK
+	atari_mouse_buttons = 0;
+#endif
+	ikbd_mouse_y0_top();
+	ikbd_mouse_thresh(mouse_threshold[0], mouse_threshold[1]);
+	ikbd_mouse_rel_pos();
+	atari_input_mouse_interrupt_hook = atamouse_interrupt;
+
+	return 0;
+}
+
+static void atamouse_close(struct input_dev *dev)
+{
+	ikbd_mouse_disable();
+	atari_input_mouse_interrupt_hook = NULL;
+}
+
+static int __init atamouse_init(void)
+{
+	int error;
+
+	if (!MACH_IS_ATARI || !ATARIHW_PRESENT(ST_MFP))
+		return -ENODEV;
+
+	error = atari_keyb_init();
+	if (error)
+		return error;
+
+	atamouse_dev = input_allocate_device();
+	if (!atamouse_dev)
+		return -ENOMEM;
+
+	atamouse_dev->name = "Atari mouse";
+	atamouse_dev->phys = "atamouse/input0";
+	atamouse_dev->id.bustype = BUS_HOST;
+	atamouse_dev->id.vendor = 0x0001;
+	atamouse_dev->id.product = 0x0002;
+	atamouse_dev->id.version = 0x0100;
+
+	atamouse_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REL);
+	atamouse_dev->relbit[0] = BIT_MASK(REL_X) | BIT_MASK(REL_Y);
+	atamouse_dev->keybit[BIT_WORD(BTN_LEFT)] = BIT_MASK(BTN_LEFT) |
+		BIT_MASK(BTN_MIDDLE) | BIT_MASK(BTN_RIGHT);
+
+	atamouse_dev->open = atamouse_open;
+	atamouse_dev->close = atamouse_close;
+
+	error = input_register_device(atamouse_dev);
+	if (error) {
+		input_free_device(atamouse_dev);
+		return error;
+	}
+
+	return 0;
+}
+
+static void __exit atamouse_exit(void)
+{
+	input_unregister_device(atamouse_dev);
+}
+
+module_init(atamouse_init);
+module_exit(atamouse_exit);