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, 176 insertions, 0 deletions

diff --git a/scripts/package/builddeb b/scripts/package/builddeb
new file mode 100755
index 000000000..ba1defc61
--- /dev/null
+++ b/scripts/package/builddeb
@@ -0,0 +1,176 @@
+#!/bin/sh
+#
+# builddeb 1.3
+# Copyright 2003 Wichert Akkerman <wichert@wiggy.net>
+#
+# Simple script to generate a deb package for a Linux kernel. All the
+# complexity of what to do with a kernel after it is installed or removed
+# is left to other scripts and packages. Scripts can be placed into the
+# preinst, postinst, prerm and postrm directories in /etc/kernel or
+# /usr/share/kernel. A different list of search directories can be given
+# via KDEB_HOOKDIR. Scripts in directories earlier in the list will
+# override scripts of the same name in later directories.  The script will
+# be called on package installation and removal.
+
+set -eu
+
+is_enabled() {
+	grep -q "^$1=y" include/config/auto.conf
+}
+
+if_enabled_echo() {
+	if is_enabled "$1"; then
+		echo -n "$2"
+	elif [ $# -ge 3 ]; then
+		echo -n "$3"
+	fi
+}
+
+install_linux_image () {
+	pname=$1
+	pdir=debian/$1
+
+	# Only some architectures with OF support have this target
+	if is_enabled CONFIG_OF_EARLY_FLATTREE && [ -d "${srctree}/arch/${SRCARCH}/boot/dts" ]; then
+		${MAKE} -f ${srctree}/Makefile INSTALL_DTBS_PATH="${pdir}/usr/lib/linux-image-${KERNELRELEASE}" dtbs_install
+	fi
+
+	${MAKE} -f ${srctree}/Makefile INSTALL_MOD_PATH="${pdir}" INSTALL_MOD_STRIP=1 modules_install
+	rm -f "${pdir}/lib/modules/${KERNELRELEASE}/build"
+
+	# Install the kernel
+	if [ "${ARCH}" = um ] ; then
+		mkdir -p "${pdir}/usr/lib/uml/modules"
+		mv "${pdir}/lib/modules/${KERNELRELEASE}" "${pdir}/usr/lib/uml/modules/${KERNELRELEASE}"
+		mkdir -p "${pdir}/usr/bin" "${pdir}/usr/share/doc/${pname}"
+		cp System.map "${pdir}/usr/lib/uml/modules/${KERNELRELEASE}/System.map"
+		cp ${KCONFIG_CONFIG} "${pdir}/usr/share/doc/${pname}/config"
+		gzip "${pdir}/usr/share/doc/${pname}/config"
+	else
+		mkdir -p "${pdir}/boot"
+		cp System.map "${pdir}/boot/System.map-${KERNELRELEASE}"
+		cp ${KCONFIG_CONFIG} "${pdir}/boot/config-${KERNELRELEASE}"
+	fi
+
+	# Not all arches have the same installed path in debian
+	# XXX: have each arch Makefile export a variable of the canonical image install
+	# path instead
+	case "${SRCARCH}" in
+	um)
+		installed_image_path="usr/bin/linux-${KERNELRELEASE}";;
+	parisc|mips|powerpc)
+		installed_image_path="boot/vmlinux-${KERNELRELEASE}";;
+	*)
+		installed_image_path="boot/vmlinuz-${KERNELRELEASE}";;
+	esac
+	cp "$(${MAKE} -s -f ${srctree}/Makefile image_name)" "${pdir}/${installed_image_path}"
+
+	if [ "${ARCH}" != um ]; then
+		install_maint_scripts "${pdir}"
+	fi
+}
+
+install_maint_scripts () {
+	# Install the maintainer scripts
+	# Note: hook scripts under /etc/kernel are also executed by official Debian
+	# kernel packages, as well as kernel packages built using make-kpkg.
+	# make-kpkg sets $INITRD to indicate whether an initramfs is wanted, and
+	# so do we; recent versions of dracut and initramfs-tools will obey this.
+	debhookdir=${KDEB_HOOKDIR:-/etc/kernel /usr/share/kernel}
+	for script in postinst postrm preinst prerm; do
+		mkdir -p "${pdir}/DEBIAN"
+		cat <<-EOF > "${pdir}/DEBIAN/${script}"
+		#!/bin/sh
+
+		set -e
+
+		# Pass maintainer script parameters to hook scripts
+		export DEB_MAINT_PARAMS="\$*"
+
+		# Tell initramfs builder whether it's wanted
+		export INITRD=$(if_enabled_echo CONFIG_BLK_DEV_INITRD Yes No)
+
+		# run-parts will error out if one of its directory arguments does not
+		# exist, so filter the list of hook directories accordingly.
+		hookdirs=
+		for dir in ${debhookdir}; do
+			test -d "\$dir/${script}.d" || continue
+			hookdirs="\$hookdirs \$dir/${script}.d"
+		done
+		hookdirs="\${hookdirs# }"
+		test -n "\$hookdirs" && run-parts --arg="${KERNELRELEASE}" --arg="/${installed_image_path}" \$hookdirs
+		exit 0
+		EOF
+		chmod 755 "${pdir}/DEBIAN/${script}"
+	done
+}
+
+install_linux_image_dbg () {
+	pdir=debian/$1
+
+	# Parse modules.order directly because 'make modules_install' may sign,
+	# compress modules, and then run unneeded depmod.
+	if is_enabled CONFIG_MODULES; then
+		while read -r mod; do
+			mod="${mod%.o}.ko"
+			dbg="${pdir}/usr/lib/debug/lib/modules/${KERNELRELEASE}/kernel/${mod}"
+			buildid=$("${READELF}" -n "${mod}" | sed -n 's@^.*Build ID: \(..\)\(.*\)@\1/\2@p')
+			link="${pdir}/usr/lib/debug/.build-id/${buildid}.debug"
+
+			mkdir -p "${dbg%/*}" "${link%/*}"
+			"${OBJCOPY}" --only-keep-debug "${mod}" "${dbg}"
+			ln -sf --relative "${dbg}" "${link}"
+		done < modules.order
+	fi
+
+	# Build debug package
+	# Different tools want the image in different locations
+	# perf
+	mkdir -p ${pdir}/usr/lib/debug/lib/modules/${KERNELRELEASE}/
+	cp vmlinux ${pdir}/usr/lib/debug/lib/modules/${KERNELRELEASE}/
+	# systemtap
+	mkdir -p ${pdir}/usr/lib/debug/boot/
+	ln -s ../lib/modules/${KERNELRELEASE}/vmlinux ${pdir}/usr/lib/debug/boot/vmlinux-${KERNELRELEASE}
+	# kdump-tools
+	ln -s lib/modules/${KERNELRELEASE}/vmlinux ${pdir}/usr/lib/debug/vmlinux-${KERNELRELEASE}
+}
+
+install_kernel_headers () {
+	pdir=debian/$1
+	version=${1#linux-headers-}
+
+	# Override $CC only for cross-compiles, to not unnecessarily rebuild
+	# scripts/ including plugins, which may lead to a full kernel rebuild.
+	if [ -n "${CROSS_COMPILE}" ]; then
+		CC="${DEB_HOST_GNU_TYPE}-gcc" "${srctree}/scripts/package/install-extmod-build" "${pdir}/usr/src/linux-headers-${version}"
+	else
+		"${srctree}/scripts/package/install-extmod-build" "${pdir}/usr/src/linux-headers-${version}"
+	fi
+
+	mkdir -p $pdir/lib/modules/$version/
+	ln -s /usr/src/linux-headers-$version $pdir/lib/modules/$version/build
+}
+
+install_libc_headers () {
+	pdir=debian/$1
+
+	$MAKE -f $srctree/Makefile headers_install INSTALL_HDR_PATH=$pdir/usr
+
+	# move asm headers to /usr/include/<libc-machine>/asm to match the structure
+	# used by Debian-based distros (to support multi-arch)
+	mkdir "$pdir/usr/include/${DEB_HOST_MULTIARCH}"
+	mv "$pdir/usr/include/asm" "$pdir/usr/include/${DEB_HOST_MULTIARCH}"
+}
+
+package=$1
+
+case "${package}" in
+*-dbg)
+	install_linux_image_dbg "${package}";;
+linux-image-*|user-mode-linux-*)
+	install_linux_image "${package}";;
+linux-libc-dev)
+	install_libc_headers "${package}";;
+linux-headers-*)
+	install_kernel_headers "${package}";;
+esac