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, 113 insertions, 0 deletions

diff --git a/drivers/input/mouse/rpcmouse.c b/drivers/input/mouse/rpcmouse.c
new file mode 100644
index 000000000..6774029e0
--- /dev/null
+++ b/drivers/input/mouse/rpcmouse.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Acorn RiscPC mouse driver for Linux/ARM
+ *
+ *  Copyright (c) 2000-2002 Vojtech Pavlik
+ *  Copyright (C) 1996-2002 Russell King
+ */
+
+/*
+ *
+ * This handles the Acorn RiscPCs mouse.  We basically have a couple of
+ * hardware registers that track the sensor count for the X-Y movement and
+ * another register holding the button state.  On every VSYNC interrupt we read
+ * the complete state and then work out if something has changed.
+ */
+
+#include <linux/module.h>
+#include <linux/ptrace.h>
+#include <linux/interrupt.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/io.h>
+
+#include <mach/hardware.h>
+#include <asm/irq.h>
+#include <asm/hardware/iomd.h>
+
+MODULE_AUTHOR("Vojtech Pavlik, Russell King");
+MODULE_DESCRIPTION("Acorn RiscPC mouse driver");
+MODULE_LICENSE("GPL");
+
+static short rpcmouse_lastx, rpcmouse_lasty;
+static struct input_dev *rpcmouse_dev;
+
+static irqreturn_t rpcmouse_irq(int irq, void *dev_id)
+{
+	struct input_dev *dev = dev_id;
+	short x, y, dx, dy, b;
+
+	x = (short) iomd_readl(IOMD_MOUSEX);
+	y = (short) iomd_readl(IOMD_MOUSEY);
+	b = (short) (__raw_readl(IOMEM(0xe0310000)) ^ 0x70);
+
+	dx = x - rpcmouse_lastx;
+	dy = y - rpcmouse_lasty;
+
+	rpcmouse_lastx = x;
+	rpcmouse_lasty = y;
+
+	input_report_rel(dev, REL_X, dx);
+	input_report_rel(dev, REL_Y, -dy);
+
+	input_report_key(dev, BTN_LEFT,   b & 0x40);
+	input_report_key(dev, BTN_MIDDLE, b & 0x20);
+	input_report_key(dev, BTN_RIGHT,  b & 0x10);
+
+	input_sync(dev);
+
+	return IRQ_HANDLED;
+}
+
+
+static int __init rpcmouse_init(void)
+{
+	int err;
+
+	rpcmouse_dev = input_allocate_device();
+	if (!rpcmouse_dev)
+		return -ENOMEM;
+
+	rpcmouse_dev->name = "Acorn RiscPC Mouse";
+	rpcmouse_dev->phys = "rpcmouse/input0";
+	rpcmouse_dev->id.bustype = BUS_HOST;
+	rpcmouse_dev->id.vendor  = 0x0005;
+	rpcmouse_dev->id.product = 0x0001;
+	rpcmouse_dev->id.version = 0x0100;
+
+	rpcmouse_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REL);
+	rpcmouse_dev->keybit[BIT_WORD(BTN_LEFT)] = BIT_MASK(BTN_LEFT) |
+		BIT_MASK(BTN_MIDDLE) | BIT_MASK(BTN_RIGHT);
+	rpcmouse_dev->relbit[0]	= BIT_MASK(REL_X) | BIT_MASK(REL_Y);
+
+	rpcmouse_lastx = (short) iomd_readl(IOMD_MOUSEX);
+	rpcmouse_lasty = (short) iomd_readl(IOMD_MOUSEY);
+
+	if (request_irq(IRQ_VSYNCPULSE, rpcmouse_irq, IRQF_SHARED, "rpcmouse", rpcmouse_dev)) {
+		printk(KERN_ERR "rpcmouse: unable to allocate VSYNC interrupt\n");
+		err = -EBUSY;
+		goto err_free_dev;
+	}
+
+	err = input_register_device(rpcmouse_dev);
+	if (err)
+		goto err_free_irq;
+
+	return 0;
+
+ err_free_irq:
+	free_irq(IRQ_VSYNCPULSE, rpcmouse_dev);
+ err_free_dev:
+	input_free_device(rpcmouse_dev);
+
+	return err;
+}
+
+static void __exit rpcmouse_exit(void)
+{
+	free_irq(IRQ_VSYNCPULSE, rpcmouse_dev);
+	input_unregister_device(rpcmouse_dev);
+}
+
+module_init(rpcmouse_init);
+module_exit(rpcmouse_exit);