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

4 files changed, 193 insertions, 0 deletions

diff --git a/arch/mips/n64/Makefile b/arch/mips/n64/Makefile
new file mode 100644
index 000000000..b64a05ae2
--- /dev/null
+++ b/arch/mips/n64/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Nintendo 64
+#
+
+obj-y := init.o irq.o
diff --git a/arch/mips/n64/Platform b/arch/mips/n64/Platform
new file mode 100644
index 000000000..246478313
--- /dev/null
+++ b/arch/mips/n64/Platform
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Nintendo 64
+#
+
+cflags-$(CONFIG_MACH_NINTENDO64)    += -I$(srctree)/arch/mips/include/asm/mach-n64
+load-$(CONFIG_MACH_NINTENDO64)      += 0xffffffff80101000
diff --git a/arch/mips/n64/init.c b/arch/mips/n64/init.c
new file mode 100644
index 000000000..66ec28ab4
--- /dev/null
+++ b/arch/mips/n64/init.c
@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Nintendo 64 init.
+ *
+ *  Copyright (C) 2021	Lauri Kasanen
+ */
+#include <linux/init.h>
+#include <linux/ioport.h>
+#include <linux/irq.h>
+#include <linux/memblock.h>
+#include <linux/platform_device.h>
+#include <linux/platform_data/simplefb.h>
+#include <linux/string.h>
+
+#include <asm/bootinfo.h>
+#include <asm/fw/fw.h>
+#include <asm/time.h>
+
+#define IO_MEM_RESOURCE_START	0UL
+#define IO_MEM_RESOURCE_END	0x1fffffffUL
+
+/*
+ * System-specifc irq names for clarity
+ */
+#define MIPS_CPU_IRQ(x)		(MIPS_CPU_IRQ_BASE + (x))
+#define MIPS_SOFTINT0_IRQ	MIPS_CPU_IRQ(0)
+#define MIPS_SOFTINT1_IRQ	MIPS_CPU_IRQ(1)
+#define RCP_IRQ			MIPS_CPU_IRQ(2)
+#define CART_IRQ		MIPS_CPU_IRQ(3)
+#define PRENMI_IRQ		MIPS_CPU_IRQ(4)
+#define RDBR_IRQ		MIPS_CPU_IRQ(5)
+#define RDBW_IRQ		MIPS_CPU_IRQ(6)
+#define TIMER_IRQ		MIPS_CPU_IRQ(7)
+
+static void __init iomem_resource_init(void)
+{
+	iomem_resource.start = IO_MEM_RESOURCE_START;
+	iomem_resource.end = IO_MEM_RESOURCE_END;
+}
+
+const char *get_system_type(void)
+{
+	return "Nintendo 64";
+}
+
+void __init prom_init(void)
+{
+	fw_init_cmdline();
+}
+
+#define W 320
+#define H 240
+#define REG_BASE ((u32 __iomem *) CKSEG1ADDR(0x4400000))
+
+static void __init n64rdp_write_reg(const u8 reg, const u32 value)
+{
+	__raw_writel(value, REG_BASE + reg);
+}
+
+#undef REG_BASE
+
+static const u32 ntsc_320[] __initconst = {
+	0x00013212, 0x00000000, 0x00000140, 0x00000200,
+	0x00000000, 0x03e52239, 0x0000020d, 0x00000c15,
+	0x0c150c15, 0x006c02ec, 0x002501ff, 0x000e0204,
+	0x00000200, 0x00000400
+};
+
+#define MI_REG_BASE 0x4300000
+#define NUM_MI_REGS 4
+#define AI_REG_BASE 0x4500000
+#define NUM_AI_REGS 6
+#define PI_REG_BASE 0x4600000
+#define NUM_PI_REGS 5
+#define SI_REG_BASE 0x4800000
+#define NUM_SI_REGS 7
+
+static int __init n64_platform_init(void)
+{
+	static const char simplefb_resname[] = "FB";
+	static const struct simplefb_platform_data mode = {
+		.width = W,
+		.height = H,
+		.stride = W * 2,
+		.format = "r5g5b5a1"
+	};
+	struct resource res[3];
+	void *orig;
+	unsigned long phys;
+	unsigned i;
+
+	memset(res, 0, sizeof(struct resource) * 3);
+	res[0].flags = IORESOURCE_MEM;
+	res[0].start = MI_REG_BASE;
+	res[0].end = MI_REG_BASE + NUM_MI_REGS * 4 - 1;
+
+	res[1].flags = IORESOURCE_MEM;
+	res[1].start = AI_REG_BASE;
+	res[1].end = AI_REG_BASE + NUM_AI_REGS * 4 - 1;
+
+	res[2].flags = IORESOURCE_IRQ;
+	res[2].start = RCP_IRQ;
+	res[2].end = RCP_IRQ;
+
+	platform_device_register_simple("n64audio", -1, res, 3);
+
+	memset(&res[0], 0, sizeof(res[0]));
+	res[0].flags = IORESOURCE_MEM;
+	res[0].start = PI_REG_BASE;
+	res[0].end = PI_REG_BASE + NUM_PI_REGS * 4 - 1;
+
+	platform_device_register_simple("n64cart", -1, res, 1);
+
+	memset(&res[0], 0, sizeof(res[0]));
+	res[0].flags = IORESOURCE_MEM;
+	res[0].start = SI_REG_BASE;
+	res[0].end = SI_REG_BASE + NUM_SI_REGS * 4 - 1;
+
+	platform_device_register_simple("n64joy", -1, res, 1);
+
+	/* The framebuffer needs 64-byte alignment */
+	orig = kzalloc(W * H * 2 + 63, GFP_DMA | GFP_KERNEL);
+	if (!orig)
+		return -ENOMEM;
+	phys = virt_to_phys(orig);
+	phys += 63;
+	phys &= ~63;
+
+	for (i = 0; i < ARRAY_SIZE(ntsc_320); i++) {
+		if (i == 1)
+			n64rdp_write_reg(i, phys);
+		else
+			n64rdp_write_reg(i, ntsc_320[i]);
+	}
+
+	/* setup IORESOURCE_MEM as framebuffer memory */
+	memset(&res[0], 0, sizeof(res[0]));
+	res[0].flags = IORESOURCE_MEM;
+	res[0].name = simplefb_resname;
+	res[0].start = phys;
+	res[0].end = phys + W * H * 2 - 1;
+
+	platform_device_register_resndata(NULL, "simple-framebuffer", 0,
+					  &res[0], 1, &mode, sizeof(mode));
+
+	return 0;
+}
+
+#undef W
+#undef H
+
+arch_initcall(n64_platform_init);
+
+void __init plat_mem_setup(void)
+{
+	iomem_resource_init();
+	memblock_add(0x0, 8 * 1024 * 1024); /* Bootloader blocks the 4mb config */
+}
+
+void __init plat_time_init(void)
+{
+	/* 93.75 MHz cpu, count register runs at half rate */
+	mips_hpt_frequency = 93750000 / 2;
+}
diff --git a/arch/mips/n64/irq.c b/arch/mips/n64/irq.c
new file mode 100644
index 000000000..1861e962d
--- /dev/null
+++ b/arch/mips/n64/irq.c
@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  N64 IRQ
+ *
+ *  Copyright (C) 2021 Lauri Kasanen
+ */
+#include <linux/export.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+
+#include <asm/irq_cpu.h>
+
+void __init arch_init_irq(void)
+{
+	mips_cpu_irq_init();
+}