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, 236 insertions, 0 deletions

diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
new file mode 100644
index 000000000..5baf1c44f
--- /dev/null
+++ b/scripts/kconfig/Makefile
@@ -0,0 +1,236 @@
+# SPDX-License-Identifier: GPL-2.0
+# ===========================================================================
+# Kernel configuration targets
+# These targets are used from top-level makefile
+
+ifdef KBUILD_KCONFIG
+Kconfig := $(KBUILD_KCONFIG)
+else
+Kconfig := Kconfig
+endif
+
+ifndef KBUILD_DEFCONFIG
+KBUILD_DEFCONFIG := defconfig
+endif
+
+ifeq ($(quiet),silent_)
+silent := -s
+endif
+
+export KCONFIG_DEFCONFIG_LIST :=
+ifndef cross_compiling
+kernel-release := $(shell uname -r)
+KCONFIG_DEFCONFIG_LIST += \
+	/lib/modules/$(kernel-release)/.config \
+	/etc/kernel-config \
+	/boot/config-$(kernel-release)
+endif
+KCONFIG_DEFCONFIG_LIST += arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)
+
+ifneq ($(findstring c, $(KBUILD_EXTRA_WARN)),)
+export KCONFIG_WARN_UNKNOWN_SYMBOLS=1
+endif
+
+ifneq ($(findstring e, $(KBUILD_EXTRA_WARN)),)
+export KCONFIG_WERROR=1
+endif
+
+# We need this, in case the user has it in its environment
+unexport CONFIG_
+
+config-prog	:= conf
+menuconfig-prog	:= mconf
+nconfig-prog	:= nconf
+gconfig-prog	:= gconf
+xconfig-prog	:= qconf
+
+define config_rule
+PHONY += $(1)
+$(1): $(obj)/$($(1)-prog)
+	$(Q)$$< $(silent) $(Kconfig)
+
+PHONY += build_$(1)
+build_$(1): $(obj)/$($(1)-prog)
+endef
+
+$(foreach c, config menuconfig nconfig gconfig xconfig, $(eval $(call config_rule,$(c))))
+
+PHONY += localmodconfig localyesconfig
+localyesconfig localmodconfig: $(obj)/conf
+	$(Q)$(PERL) $(src)/streamline_config.pl --$@ $(srctree) $(Kconfig) > .tmp.config
+	$(Q)if [ -f .config ]; then 				\
+		cmp -s .tmp.config .config ||			\
+		(mv -f .config .config.old.1;			\
+		 mv -f .tmp.config .config;			\
+		 $< $(silent) --oldconfig $(Kconfig);		\
+		 mv -f .config.old.1 .config.old)		\
+	else							\
+		mv -f .tmp.config .config;			\
+		$< $(silent) --oldconfig $(Kconfig);		\
+	fi
+	$(Q)rm -f .tmp.config
+
+# These targets map 1:1 to the commandline options of 'conf'
+#
+# Note:
+#  syncconfig has become an internal implementation detail and is now
+#  deprecated for external use
+simple-targets := oldconfig allnoconfig allyesconfig allmodconfig \
+	alldefconfig randconfig listnewconfig olddefconfig syncconfig \
+	helpnewconfig yes2modconfig mod2yesconfig mod2noconfig
+
+PHONY += $(simple-targets)
+
+$(simple-targets): $(obj)/conf
+	$(Q)$< $(silent) --$@ $(Kconfig)
+
+PHONY += savedefconfig defconfig
+
+savedefconfig: $(obj)/conf
+	$(Q)$< $(silent) --$@=defconfig $(Kconfig)
+
+defconfig: $(obj)/conf
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)),)
+	@$(kecho) "*** Default configuration is based on '$(KBUILD_DEFCONFIG)'"
+	$(Q)$< $(silent) --defconfig=arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG) $(Kconfig)
+else
+	@$(kecho) "*** Default configuration is based on target '$(KBUILD_DEFCONFIG)'"
+	$(Q)$(MAKE) -f $(srctree)/Makefile $(KBUILD_DEFCONFIG)
+endif
+
+%_defconfig: $(obj)/conf
+	$(Q)$< $(silent) --defconfig=arch/$(SRCARCH)/configs/$@ $(Kconfig)
+
+configfiles = $(wildcard $(srctree)/kernel/configs/$(1) $(srctree)/arch/$(SRCARCH)/configs/$(1))
+all-config-fragments = $(call configfiles,*.config)
+config-fragments = $(call configfiles,$@)
+
+cmd_merge_fragments = $(srctree)/scripts/kconfig/merge_config.sh -m $(KCONFIG_CONFIG) $(config-fragments)
+
+%.config: $(obj)/conf
+	$(if $(config-fragments),, $(error $@ fragment does not exists on this architecture))
+	$(call cmd,merge_fragments)
+	$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
+
+PHONY += tinyconfig
+tinyconfig:
+	$(Q)KCONFIG_ALLCONFIG=kernel/configs/tiny-base.config $(MAKE) -f $(srctree)/Makefile allnoconfig
+	$(Q)$(MAKE) -f $(srctree)/Makefile tiny.config
+
+# CHECK: -o cache_dir=<path> working?
+PHONY += testconfig
+testconfig: $(obj)/conf
+	$(Q)$(PYTHON3) -B -m pytest $(src)/tests \
+	-o cache_dir=$(abspath $(obj)/tests/.cache) \
+	$(if $(findstring 1,$(KBUILD_VERBOSE)),--capture=no)
+clean-files += tests/.cache
+
+# Help text used by make help
+help:
+	@echo  'Configuration targets:'
+	@echo  '  config	  - Update current config utilising a line-oriented program'
+	@echo  '  nconfig         - Update current config utilising a ncurses menu based program'
+	@echo  '  menuconfig	  - Update current config utilising a menu based program'
+	@echo  '  xconfig	  - Update current config utilising a Qt based front-end'
+	@echo  '  gconfig	  - Update current config utilising a GTK+ based front-end'
+	@echo  '  oldconfig	  - Update current config utilising a provided .config as base'
+	@echo  '  localmodconfig  - Update current config disabling modules not loaded'
+	@echo  '                    except those preserved by LMC_KEEP environment variable'
+	@echo  '  localyesconfig  - Update current config converting local mods to core'
+	@echo  '                    except those preserved by LMC_KEEP environment variable'
+	@echo  '  defconfig	  - New config with default from ARCH supplied defconfig'
+	@echo  '  savedefconfig   - Save current config as ./defconfig (minimal config)'
+	@echo  '  allnoconfig	  - New config where all options are answered with no'
+	@echo  '  allyesconfig	  - New config where all options are accepted with yes'
+	@echo  '  allmodconfig	  - New config selecting modules when possible'
+	@echo  '  alldefconfig    - New config with all symbols set to default'
+	@echo  '  randconfig	  - New config with random answer to all options'
+	@echo  '  yes2modconfig	  - Change answers from yes to mod if possible'
+	@echo  '  mod2yesconfig	  - Change answers from mod to yes if possible'
+	@echo  '  mod2noconfig	  - Change answers from mod to no if possible'
+	@echo  '  listnewconfig   - List new options'
+	@echo  '  helpnewconfig   - List new options and help text'
+	@echo  '  olddefconfig	  - Same as oldconfig but sets new symbols to their'
+	@echo  '                    default value without prompting'
+	@echo  '  tinyconfig	  - Configure the tiniest possible kernel'
+	@echo  '  testconfig	  - Run Kconfig unit tests (requires python3 and pytest)'
+	@echo  ''
+	@echo  'Configuration topic targets:'
+	@$(foreach f, $(all-config-fragments), \
+		if help=$$(grep -m1 '^# Help: ' $(f)); then \
+			printf '  %-25s - %s\n' '$(notdir $(f))' "$${help#*: }"; \
+		fi;)
+
+# ===========================================================================
+# object files used by all kconfig flavours
+common-objs	:= confdata.o expr.o lexer.lex.o menu.o parser.tab.o \
+		   preprocess.o symbol.o util.o
+
+$(obj)/lexer.lex.o: $(obj)/parser.tab.h
+HOSTCFLAGS_lexer.lex.o	:= -I $(src)
+HOSTCFLAGS_parser.tab.o	:= -I $(src)
+
+# conf: Used for defconfig, oldconfig and related targets
+hostprogs	+= conf
+conf-objs	:= conf.o $(common-objs)
+
+# nconf: Used for the nconfig target based on ncurses
+hostprogs	+= nconf
+nconf-objs	:= nconf.o nconf.gui.o mnconf-common.o $(common-objs)
+
+HOSTLDLIBS_nconf       = $(call read-file, $(obj)/nconf-libs)
+HOSTCFLAGS_nconf.o     = $(call read-file, $(obj)/nconf-cflags)
+HOSTCFLAGS_nconf.gui.o = $(call read-file, $(obj)/nconf-cflags)
+
+$(obj)/nconf: | $(obj)/nconf-libs
+$(obj)/nconf.o $(obj)/nconf.gui.o: | $(obj)/nconf-cflags
+
+# mconf: Used for the menuconfig target based on lxdialog
+hostprogs	+= mconf
+lxdialog	:= $(addprefix lxdialog/, \
+		     checklist.o inputbox.o menubox.o textbox.o util.o yesno.o)
+mconf-objs	:= mconf.o $(lxdialog) mnconf-common.o $(common-objs)
+
+HOSTLDLIBS_mconf = $(call read-file, $(obj)/mconf-libs)
+$(foreach f, mconf.o $(lxdialog), \
+  $(eval HOSTCFLAGS_$f = $$(call read-file, $(obj)/mconf-cflags)))
+
+$(obj)/mconf: | $(obj)/mconf-libs
+$(addprefix $(obj)/, mconf.o $(lxdialog)): | $(obj)/mconf-cflags
+
+# qconf: Used for the xconfig target based on Qt
+hostprogs	+= qconf
+qconf-cxxobjs	:= qconf.o qconf-moc.o
+qconf-objs	:= $(common-objs)
+
+HOSTLDLIBS_qconf         = $(call read-file, $(obj)/qconf-libs)
+HOSTCXXFLAGS_qconf.o     = -std=c++11 -fPIC $(call read-file, $(obj)/qconf-cflags)
+HOSTCXXFLAGS_qconf-moc.o = -std=c++11 -fPIC $(call read-file, $(obj)/qconf-cflags)
+$(obj)/qconf: | $(obj)/qconf-libs
+$(obj)/qconf.o $(obj)/qconf-moc.o: | $(obj)/qconf-cflags
+
+quiet_cmd_moc = MOC     $@
+      cmd_moc = $(call read-file, $(obj)/qconf-bin)/moc $< -o $@
+
+$(obj)/qconf-moc.cc: $(src)/qconf.h FORCE | $(obj)/qconf-bin
+	$(call if_changed,moc)
+
+targets += qconf-moc.cc
+
+# gconf: Used for the gconfig target based on GTK+
+hostprogs	+= gconf
+gconf-objs	:= gconf.o $(common-objs)
+
+HOSTLDLIBS_gconf   = $(call read-file, $(obj)/gconf-libs)
+HOSTCFLAGS_gconf.o = $(call read-file, $(obj)/gconf-cflags)
+
+$(obj)/gconf: | $(obj)/gconf-libs
+$(obj)/gconf.o: | $(obj)/gconf-cflags
+
+# check if necessary packages are available, and configure build flags
+cmd_conf_cfg = $< $(addprefix $(obj)/$*conf-, cflags libs bin); touch $(obj)/$*conf-bin
+
+$(obj)/%conf-cflags $(obj)/%conf-libs $(obj)/%conf-bin: $(src)/%conf-cfg.sh
+	$(call cmd,conf_cfg)
+
+clean-files += *conf-cflags *conf-libs *conf-bin