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, 196 insertions, 0 deletions

diff --git a/drivers/input/matrix-keymap.c b/drivers/input/matrix-keymap.c
new file mode 100644
index 000000000..3bea3575a
--- /dev/null
+++ b/drivers/input/matrix-keymap.c
@@ -0,0 +1,196 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Helpers for matrix keyboard bindings
+ *
+ * Copyright (C) 2012 Google, Inc
+ *
+ * Author:
+ *	Olof Johansson <olof@lixom.net>
+ */
+
+#include <linux/device.h>
+#include <linux/export.h>
+#include <linux/gfp.h>
+#include <linux/input.h>
+#include <linux/input/matrix_keypad.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+static bool matrix_keypad_map_key(struct input_dev *input_dev,
+				  unsigned int rows, unsigned int cols,
+				  unsigned int row_shift, unsigned int key)
+{
+	unsigned short *keymap = input_dev->keycode;
+	unsigned int row = KEY_ROW(key);
+	unsigned int col = KEY_COL(key);
+	unsigned short code = KEY_VAL(key);
+
+	if (row >= rows || col >= cols) {
+		dev_err(input_dev->dev.parent,
+			"%s: invalid keymap entry 0x%x (row: %d, col: %d, rows: %d, cols: %d)\n",
+			__func__, key, row, col, rows, cols);
+		return false;
+	}
+
+	keymap[MATRIX_SCAN_CODE(row, col, row_shift)] = code;
+	__set_bit(code, input_dev->keybit);
+
+	return true;
+}
+
+/**
+ * matrix_keypad_parse_properties() - Read properties of matrix keypad
+ *
+ * @dev: Device containing properties
+ * @rows: Returns number of matrix rows
+ * @cols: Returns number of matrix columns
+ * @return 0 if OK, <0 on error
+ */
+int matrix_keypad_parse_properties(struct device *dev,
+				   unsigned int *rows, unsigned int *cols)
+{
+	*rows = *cols = 0;
+
+	device_property_read_u32(dev, "keypad,num-rows", rows);
+	device_property_read_u32(dev, "keypad,num-columns", cols);
+
+	if (!*rows || !*cols) {
+		dev_err(dev, "number of keypad rows/columns not specified\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(matrix_keypad_parse_properties);
+
+static int matrix_keypad_parse_keymap(const char *propname,
+				      unsigned int rows, unsigned int cols,
+				      struct input_dev *input_dev)
+{
+	struct device *dev = input_dev->dev.parent;
+	unsigned int row_shift = get_count_order(cols);
+	unsigned int max_keys = rows << row_shift;
+	int i;
+	int size;
+	int error;
+
+	if (!propname)
+		propname = "linux,keymap";
+
+	size = device_property_count_u32(dev, propname);
+	if (size <= 0) {
+		dev_err(dev, "missing or malformed property %s: %d\n",
+			propname, size);
+		return size < 0 ? size : -EINVAL;
+	}
+
+	if (size > max_keys) {
+		dev_err(dev, "%s size overflow (%d vs max %u)\n",
+			propname, size, max_keys);
+		return -EINVAL;
+	}
+
+	u32 *keys __free(kfree) = kmalloc_array(size, sizeof(*keys), GFP_KERNEL);
+	if (!keys)
+		return -ENOMEM;
+
+	error = device_property_read_u32_array(dev, propname, keys, size);
+	if (error) {
+		dev_err(dev, "failed to read %s property: %d\n",
+			propname, error);
+		return error;
+	}
+
+	for (i = 0; i < size; i++) {
+		if (!matrix_keypad_map_key(input_dev, rows, cols,
+					   row_shift, keys[i]))
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * matrix_keypad_build_keymap - convert platform keymap into matrix keymap
+ * @keymap_data: keymap supplied by the platform code
+ * @keymap_name: name of device tree property containing keymap (if device
+ *	tree support is enabled).
+ * @rows: number of rows in target keymap array
+ * @cols: number of cols in target keymap array
+ * @keymap: expanded version of keymap that is suitable for use by
+ * matrix keyboard driver
+ * @input_dev: input devices for which we are setting up the keymap
+ *
+ * This function converts platform keymap (encoded with KEY() macro) into
+ * an array of keycodes that is suitable for using in a standard matrix
+ * keyboard driver that uses row and col as indices.
+ *
+ * If @keymap_data is not supplied and device tree support is enabled
+ * it will attempt load the keymap from property specified by @keymap_name
+ * argument (or "linux,keymap" if @keymap_name is %NULL).
+ *
+ * If @keymap is %NULL the function will automatically allocate managed
+ * block of memory to store the keymap. This memory will be associated with
+ * the parent device and automatically freed when device unbinds from the
+ * driver.
+ *
+ * Callers are expected to set up input_dev->dev.parent before calling this
+ * function.
+ */
+int matrix_keypad_build_keymap(const struct matrix_keymap_data *keymap_data,
+			       const char *keymap_name,
+			       unsigned int rows, unsigned int cols,
+			       unsigned short *keymap,
+			       struct input_dev *input_dev)
+{
+	unsigned int row_shift = get_count_order(cols);
+	size_t max_keys = rows << row_shift;
+	int i;
+	int error;
+
+	if (WARN_ON(!input_dev->dev.parent))
+		return -EINVAL;
+
+	if (!keymap) {
+		keymap = devm_kcalloc(input_dev->dev.parent,
+				      max_keys, sizeof(*keymap),
+				      GFP_KERNEL);
+		if (!keymap) {
+			dev_err(input_dev->dev.parent,
+				"Unable to allocate memory for keymap");
+			return -ENOMEM;
+		}
+	}
+
+	input_dev->keycode = keymap;
+	input_dev->keycodesize = sizeof(*keymap);
+	input_dev->keycodemax = max_keys;
+
+	__set_bit(EV_KEY, input_dev->evbit);
+
+	if (keymap_data) {
+		for (i = 0; i < keymap_data->keymap_size; i++) {
+			unsigned int key = keymap_data->keymap[i];
+
+			if (!matrix_keypad_map_key(input_dev, rows, cols,
+						   row_shift, key))
+				return -EINVAL;
+		}
+	} else {
+		error = matrix_keypad_parse_keymap(keymap_name, rows, cols,
+						   input_dev);
+		if (error)
+			return error;
+	}
+
+	__clear_bit(KEY_RESERVED, input_dev->keybit);
+
+	return 0;
+}
+EXPORT_SYMBOL(matrix_keypad_build_keymap);
+
+MODULE_DESCRIPTION("Helpers for matrix keyboard bindings");
+MODULE_LICENSE("GPL");