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, 134 insertions, 0 deletions

diff --git a/arch/m68k/Makefile b/arch/m68k/Makefile
new file mode 100644
index 000000000..0abcf994c
--- /dev/null
+++ b/arch/m68k/Makefile
@@ -0,0 +1,134 @@
+#
+# m68k/Makefile
+#
+# This file is included by the global makefile so that you can add your own
+# architecture-specific flags and dependencies.
+#
+# 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) 1994 by Hamish Macdonald
+# Copyright (C) 2002,2011 Greg Ungerer <gerg@snapgear.com>
+#
+
+KBUILD_DEFCONFIG := multi_defconfig
+
+ifdef cross_compiling
+    ifeq ($(CROSS_COMPILE),)
+		CROSS_COMPILE := $(call cc-cross-prefix, \
+			m68k-linux-gnu- m68k-linux- m68k-unknown-linux-gnu-)
+    endif
+endif
+
+#
+#	Enable processor type. Ordering of these is important - we want to
+#	use the minimum processor type of the range we support. The logic
+#	for 680x0 will only allow use of the -m68060 or -m68040 if no other
+#	680x0 type is specified - and no option is specified for 68030 or
+#	68020. The other m68k/ColdFire types always specify some type of
+#	compiler cpu type flag.
+#
+ifndef CONFIG_M68040
+cpuflags-$(CONFIG_M68060)	= -m68060
+endif
+ifndef CONFIG_M68060
+cpuflags-$(CONFIG_M68040)	= -m68040
+endif
+cpuflags-$(CONFIG_M68030)	=
+cpuflags-$(CONFIG_M68020)	=
+cpuflags-$(CONFIG_M68000)	= -m68000
+cpuflags-$(CONFIG_M5441x)	= $(call cc-option,-mcpu=54455,-mcfv4e)
+cpuflags-$(CONFIG_M54xx)	= $(call cc-option,-mcpu=5475,-m5200)
+cpuflags-$(CONFIG_M5407)	= $(call cc-option,-mcpu=5407,-m5200)
+cpuflags-$(CONFIG_M532x)	= $(call cc-option,-mcpu=532x,-m5307)
+cpuflags-$(CONFIG_M537x)	= $(call cc-option,-mcpu=537x,-m5307)
+cpuflags-$(CONFIG_M5307)	= $(call cc-option,-mcpu=5307,-m5200)
+cpuflags-$(CONFIG_M528x)	= $(call cc-option,-mcpu=528x,-m5307)
+cpuflags-$(CONFIG_M5275)	= $(call cc-option,-mcpu=5275,-m5307)
+cpuflags-$(CONFIG_M5272)	= $(call cc-option,-mcpu=5272,-m5307)
+cpuflags-$(CONFIG_M5271)	= $(call cc-option,-mcpu=5271,-m5307)
+cpuflags-$(CONFIG_M523x)	= $(call cc-option,-mcpu=523x,-m5307)
+cpuflags-$(CONFIG_M525x)	= $(call cc-option,-mcpu=5253,-m5200)
+cpuflags-$(CONFIG_M5249)	= $(call cc-option,-mcpu=5249,-m5200)
+cpuflags-$(CONFIG_M520x)	= $(call cc-option,-mcpu=5208,-m5200)
+cpuflags-$(CONFIG_M5206e)	= $(call cc-option,-mcpu=5206e,-m5200)
+cpuflags-$(CONFIG_M5206)	= $(call cc-option,-mcpu=5206,-m5200)
+
+# Evaluate tune cc-option calls now
+cpuflags-y := $(cpuflags-y)
+
+KBUILD_AFLAGS += $(cpuflags-y)
+KBUILD_CFLAGS += $(cpuflags-y)
+
+KBUILD_CFLAGS += -pipe -ffreestanding
+
+ifdef CONFIG_MMU
+KBUILD_CFLAGS += -ffixed-a2
+else
+# we can use a m68k-linux-gcc toolchain with these in place
+KBUILD_CPPFLAGS += -DUTS_SYSNAME=\"uClinux\"
+KBUILD_CPPFLAGS += -D__uClinux__
+endif
+
+KBUILD_LDFLAGS := -m m68kelf
+
+ifdef CONFIG_SUN3
+LDFLAGS_vmlinux = -N
+endif
+
+CHECKFLAGS += -D__mc68000__
+
+
+ifdef CONFIG_KGDB
+# If configured for kgdb support, include debugging infos and keep the
+# frame pointer
+KBUILD_CFLAGS := $(subst -fomit-frame-pointer,,$(KBUILD_CFLAGS)) -g
+endif
+
+libs-y				+= arch/m68k/lib/
+
+
+all:	zImage
+
+lilo:	vmlinux
+	if [ -f $(INSTALL_PATH)/vmlinux ]; then mv -f $(INSTALL_PATH)/vmlinux $(INSTALL_PATH)/vmlinux.old; fi
+	if [ -f $(INSTALL_PATH)/System.map ]; then mv -f $(INSTALL_PATH)/System.map $(INSTALL_PATH)/System.old; fi
+	cat vmlinux > $(INSTALL_PATH)/vmlinux
+	cp System.map $(INSTALL_PATH)/System.map
+	if [ -x /sbin/lilo ]; then /sbin/lilo; else /etc/lilo/install; fi
+
+zImage compressed: vmlinux.gz
+
+vmlinux.gz: vmlinux
+
+ifndef CONFIG_KGDB
+	cp vmlinux vmlinux.tmp
+	$(STRIP) vmlinux.tmp
+	$(KGZIP) -9c vmlinux.tmp >vmlinux.gz
+	rm vmlinux.tmp
+else
+	$(KGZIP) -9c vmlinux >vmlinux.gz
+endif
+
+bzImage: vmlinux.bz2
+
+vmlinux.bz2: vmlinux
+
+ifndef CONFIG_KGDB
+	cp vmlinux vmlinux.tmp
+	$(STRIP) vmlinux.tmp
+	$(KBZIP2) -1c vmlinux.tmp >vmlinux.bz2
+	rm vmlinux.tmp
+else
+	$(KBZIP2) -1c vmlinux >vmlinux.bz2
+endif
+
+CLEAN_FILES += vmlinux.gz vmlinux.bz2
+
+archheaders:
+	$(Q)$(MAKE) $(build)=arch/m68k/kernel/syscalls all
+
+install: KBUILD_IMAGE := vmlinux.gz
+install:
+	$(call cmd,install)