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, 60 insertions, 0 deletions

diff --git a/arch/mips/bcm63xx/dev-spi.c b/arch/mips/bcm63xx/dev-spi.c
new file mode 100644
index 000000000..232385441
--- /dev/null
+++ b/arch/mips/bcm63xx/dev-spi.c
@@ -0,0 +1,60 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2009-2011 Florian Fainelli <florian@openwrt.org>
+ * Copyright (C) 2010 Tanguy Bouzeloc <tanguy.bouzeloc@efixo.com>
+ */
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/platform_device.h>
+#include <linux/err.h>
+#include <linux/clk.h>
+
+#include <bcm63xx_cpu.h>
+#include <bcm63xx_dev_spi.h>
+#include <bcm63xx_regs.h>
+
+static struct resource spi_resources[] = {
+	{
+		.start		= -1, /* filled at runtime */
+		.end		= -1, /* filled at runtime */
+		.flags		= IORESOURCE_MEM,
+	},
+	{
+		.start		= -1, /* filled at runtime */
+		.flags		= IORESOURCE_IRQ,
+	},
+};
+
+static struct platform_device bcm63xx_spi_device = {
+	.id		= -1,
+	.num_resources	= ARRAY_SIZE(spi_resources),
+	.resource	= spi_resources,
+};
+
+int __init bcm63xx_spi_register(void)
+{
+	if (BCMCPU_IS_6328() || BCMCPU_IS_6345())
+		return -ENODEV;
+
+	spi_resources[0].start = bcm63xx_regset_address(RSET_SPI);
+	spi_resources[0].end = spi_resources[0].start;
+	spi_resources[1].start = bcm63xx_get_irq_number(IRQ_SPI);
+
+	if (BCMCPU_IS_6338() || BCMCPU_IS_6348()) {
+		bcm63xx_spi_device.name = "bcm6348-spi",
+		spi_resources[0].end += BCM_6348_RSET_SPI_SIZE - 1;
+	}
+
+	if (BCMCPU_IS_3368() || BCMCPU_IS_6358() || BCMCPU_IS_6362() ||
+		BCMCPU_IS_6368()) {
+		bcm63xx_spi_device.name = "bcm6358-spi",
+		spi_resources[0].end += BCM_6358_RSET_SPI_SIZE - 1;
+	}
+
+	return platform_device_register(&bcm63xx_spi_device);
+}