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, 152 insertions, 0 deletions

diff --git a/drivers/mfd/max77714.c b/drivers/mfd/max77714.c
new file mode 100644
index 000000000..c618605a3
--- /dev/null
+++ b/drivers/mfd/max77714.c
@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Maxim MAX77714 Core Driver
+ *
+ * Copyright (C) 2022 Luca Ceresoli
+ * Author: Luca Ceresoli <luca.ceresoli@bootlin.com>
+ */
+
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/max77714.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+
+static const struct mfd_cell max77714_cells[] = {
+	{ .name = "max77714-watchdog" },
+	{ .name = "max77714-rtc" },
+};
+
+static const struct regmap_range max77714_readable_ranges[] = {
+	regmap_reg_range(MAX77714_INT_TOP,     MAX77714_INT_TOP),
+	regmap_reg_range(MAX77714_INT_TOPM,    MAX77714_INT_TOPM),
+	regmap_reg_range(MAX77714_32K_STATUS,  MAX77714_32K_CONFIG),
+	regmap_reg_range(MAX77714_CNFG_GLBL2,  MAX77714_CNFG2_ONOFF),
+};
+
+static const struct regmap_range max77714_writable_ranges[] = {
+	regmap_reg_range(MAX77714_INT_TOPM,    MAX77714_INT_TOPM),
+	regmap_reg_range(MAX77714_32K_CONFIG,  MAX77714_32K_CONFIG),
+	regmap_reg_range(MAX77714_CNFG_GLBL2,  MAX77714_CNFG2_ONOFF),
+};
+
+static const struct regmap_access_table max77714_readable_table = {
+	.yes_ranges = max77714_readable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(max77714_readable_ranges),
+};
+
+static const struct regmap_access_table max77714_writable_table = {
+	.yes_ranges = max77714_writable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(max77714_writable_ranges),
+};
+
+static const struct regmap_config max77714_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = MAX77714_CNFG2_ONOFF,
+	.rd_table = &max77714_readable_table,
+	.wr_table = &max77714_writable_table,
+};
+
+static const struct regmap_irq max77714_top_irqs[] = {
+	REGMAP_IRQ_REG(MAX77714_IRQ_TOP_ONOFF,   0, MAX77714_INT_TOP_ONOFF),
+	REGMAP_IRQ_REG(MAX77714_IRQ_TOP_RTC,     0, MAX77714_INT_TOP_RTC),
+	REGMAP_IRQ_REG(MAX77714_IRQ_TOP_GPIO,    0, MAX77714_INT_TOP_GPIO),
+	REGMAP_IRQ_REG(MAX77714_IRQ_TOP_LDO,     0, MAX77714_INT_TOP_LDO),
+	REGMAP_IRQ_REG(MAX77714_IRQ_TOP_SD,      0, MAX77714_INT_TOP_SD),
+	REGMAP_IRQ_REG(MAX77714_IRQ_TOP_GLBL,    0, MAX77714_INT_TOP_GLBL),
+};
+
+static const struct regmap_irq_chip max77714_irq_chip = {
+	.name			= "max77714-pmic",
+	.status_base		= MAX77714_INT_TOP,
+	.mask_base		= MAX77714_INT_TOPM,
+	.num_regs		= 1,
+	.irqs			= max77714_top_irqs,
+	.num_irqs		= ARRAY_SIZE(max77714_top_irqs),
+};
+
+/*
+ * MAX77714 initially uses the internal, low precision oscillator. Enable
+ * the external oscillator by setting the XOSC_RETRY bit. If the external
+ * oscillator is not OK (probably not installed) this has no effect.
+ */
+static int max77714_setup_xosc(struct device *dev, struct regmap *regmap)
+{
+	/* Internal Crystal Load Capacitance, indexed by value of 32KLOAD bits */
+	static const unsigned int load_cap[4] = {0, 10, 12, 22}; /* pF */
+	unsigned int load_cap_idx;
+	unsigned int status;
+	int err;
+
+	err = regmap_update_bits(regmap, MAX77714_32K_CONFIG,
+				 MAX77714_32K_CONFIG_XOSC_RETRY,
+				 MAX77714_32K_CONFIG_XOSC_RETRY);
+	if (err)
+		return dev_err_probe(dev, err, "Failed to configure the external oscillator\n");
+
+	err = regmap_read(regmap, MAX77714_32K_STATUS, &status);
+	if (err)
+		return dev_err_probe(dev, err, "Failed to read external oscillator status\n");
+
+	load_cap_idx = (status >> MAX77714_32K_STATUS_32KLOAD_SHF)
+		& MAX77714_32K_STATUS_32KLOAD_MSK;
+
+	dev_info(dev, "Using %s oscillator, %d pF load cap\n",
+		 status & MAX77714_32K_STATUS_32KSOURCE ? "internal" : "external",
+		 load_cap[load_cap_idx]);
+
+	return 0;
+}
+
+static int max77714_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct regmap *regmap;
+	struct regmap_irq_chip_data *irq_data;
+	int err;
+
+	regmap = devm_regmap_init_i2c(client, &max77714_regmap_config);
+	if (IS_ERR(regmap))
+		return dev_err_probe(dev, PTR_ERR(regmap),
+				     "Failed to initialise regmap\n");
+
+	err = max77714_setup_xosc(dev, regmap);
+	if (err)
+		return err;
+
+	err = devm_regmap_add_irq_chip(dev, regmap, client->irq,
+				       IRQF_ONESHOT | IRQF_SHARED, 0,
+				       &max77714_irq_chip, &irq_data);
+	if (err)
+		return dev_err_probe(dev, err, "Failed to add PMIC IRQ chip\n");
+
+	err =  devm_mfd_add_devices(dev, PLATFORM_DEVID_NONE,
+				    max77714_cells, ARRAY_SIZE(max77714_cells),
+				    NULL, 0, NULL);
+	if (err)
+		return dev_err_probe(dev, err, "Failed to register child devices\n");
+
+	return 0;
+}
+
+static const struct of_device_id max77714_dt_match[] = {
+	{ .compatible = "maxim,max77714" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, max77714_dt_match);
+
+static struct i2c_driver max77714_driver = {
+	.driver = {
+		.name = "max77714",
+		.of_match_table = max77714_dt_match,
+	},
+	.probe = max77714_probe,
+};
+module_i2c_driver(max77714_driver);
+
+MODULE_DESCRIPTION("Maxim MAX77714 MFD core driver");
+MODULE_AUTHOR("Luca Ceresoli <luca.ceresoli@bootlin.com>");
+MODULE_LICENSE("GPL");