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, 151 insertions, 0 deletions

diff --git a/arch/xtensa/boot/boot-elf/.gitignore b/arch/xtensa/boot/boot-elf/.gitignore
new file mode 100644
index 000000000..747340450
--- /dev/null
+++ b/arch/xtensa/boot/boot-elf/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+boot.lds
diff --git a/arch/xtensa/boot/boot-elf/Makefile b/arch/xtensa/boot/boot-elf/Makefile
new file mode 100644
index 000000000..faec20029
--- /dev/null
+++ b/arch/xtensa/boot/boot-elf/Makefile
@@ -0,0 +1,30 @@
+#
+# 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.
+#
+
+OBJCOPY_ARGS := -O $(if $(CONFIG_CPU_BIG_ENDIAN),elf32-xtensa-be,elf32-xtensa-le)
+
+CPPFLAGS_boot.lds += -P -C
+KBUILD_AFLAGS += -mtext-section-literals
+
+boot-y		:= bootstrap.o
+targets		+= $(boot-y) boot.lds
+
+OBJS		:= $(addprefix $(obj)/,$(boot-y))
+
+$(obj)/Image.o: $(obj)/../vmlinux.bin $(OBJS)
+	$(Q)$(OBJCOPY) $(OBJCOPY_ARGS) -R .comment \
+		--add-section image=$< \
+		--set-section-flags image=contents,alloc,load,load,data \
+		$(OBJS) $@
+
+$(obj)/../Image.elf: $(obj)/Image.o $(obj)/boot.lds
+	$(Q)$(LD) $(KBUILD_LDFLAGS) \
+		-T $(obj)/boot.lds \
+		--build-id=none \
+		-o $@ $(obj)/Image.o
+	$(Q)$(kecho) '  Kernel: $@ is ready'
+
+all Image: $(obj)/../Image.elf
diff --git a/arch/xtensa/boot/boot-elf/boot.lds.S b/arch/xtensa/boot/boot-elf/boot.lds.S
new file mode 100644
index 000000000..32a3b7c5b
--- /dev/null
+++ b/arch/xtensa/boot/boot-elf/boot.lds.S
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/arch/xtensa/boot/boot-elf/boot.lds.S
+ *
+ *  Copyright (C) 2008 - 2013 by Tensilica Inc.
+ *
+ *  Chris Zankel <chris@zankel.net>
+ *  Marc Gauthier <marc@tensilica.com
+ *  Pete Delaney <piet@tensilica.com>
+ */
+
+#include <asm/vectors.h>
+OUTPUT_ARCH(xtensa)
+ENTRY(_ResetVector)
+
+SECTIONS
+{
+	.ResetVector.text XCHAL_RESET_VECTOR_VADDR :
+	{
+		*(.ResetVector.text)
+	}
+
+	.image KERNELOFFSET: AT (CONFIG_KERNEL_LOAD_ADDRESS)
+	{
+		_image_start = .;
+		*(image)
+		. = (. + 3) & ~ 3;
+		_image_end = .	;
+	}
+
+	.bss ((LOADADDR(.image) + SIZEOF(.image) + 3) & ~ 3):
+	{
+		__bss_start = .;
+		*(.sbss)
+		*(.scommon)
+		*(.dynbss)
+		*(.bss)
+		__bss_end = .;
+	}
+}
diff --git a/arch/xtensa/boot/boot-elf/bootstrap.S b/arch/xtensa/boot/boot-elf/bootstrap.S
new file mode 100644
index 000000000..2dd28931d
--- /dev/null
+++ b/arch/xtensa/boot/boot-elf/bootstrap.S
@@ -0,0 +1,79 @@
+/*
+ * arch/xtensa/boot/boot-elf/bootstrap.S
+ *
+ * Low-level exception handling
+ *
+ * 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) 2004 - 2013 by Tensilica Inc.
+ *
+ * Chris Zankel <chris@zankel.net>
+ * Marc Gauthier <marc@tensilica.com>
+ * Piet Delaney <piet@tensilica.com>
+ */
+
+#include <asm/bootparam.h>
+#include <asm/initialize_mmu.h>
+#include <asm/vectors.h>
+#include <linux/linkage.h>
+
+	.section	.ResetVector.text, "ax"
+	.global         _ResetVector
+	.global         reset
+
+_ResetVector:
+	_j _SetupMMU
+
+	.begin  no-absolute-literals
+	.literal_position
+
+#ifdef CONFIG_PARSE_BOOTPARAM
+	.align 4
+_bootparam:
+	.short	BP_TAG_FIRST
+	.short	4
+	.long	BP_VERSION
+	.short	BP_TAG_LAST
+	.short	0
+	.long	0
+#endif
+
+	.align  4
+_SetupMMU:
+#if XCHAL_HAVE_WINDOWED
+	movi	a0, 0
+	wsr	a0, windowbase
+	rsync
+	movi	a0, 1
+	wsr	a0, windowstart
+	rsync
+#endif
+	movi	a0, 0x1F
+	wsr	a0, ps
+	rsync
+
+#ifndef CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX
+	initialize_mmu
+#endif
+
+	rsil    a0, XCHAL_DEBUGLEVEL-1
+	rsync
+reset:
+#if defined(CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX) && \
+	XCHAL_HAVE_PTP_MMU && XCHAL_HAVE_SPANNING_WAY
+	movi	a0, CONFIG_KERNEL_LOAD_ADDRESS
+#else
+	movi	a0, KERNELOFFSET
+#endif
+#ifdef CONFIG_PARSE_BOOTPARAM
+	movi	a2, _bootparam
+#else
+	movi	a2, 0
+#endif
+	movi	a3, 0
+	movi	a4, 0
+	jx      a0
+
+	.end    no-absolute-literals