sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.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