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, 273 insertions, 0 deletions

diff --git a/scripts/package/mkdebian b/scripts/package/mkdebian
new file mode 100755
index 000000000..d4b007b38
--- /dev/null
+++ b/scripts/package/mkdebian
@@ -0,0 +1,273 @@
+#!/bin/sh
+#
+# Copyright 2003 Wichert Akkerman <wichert@wiggy.net>
+#
+# Simple script to generate a debian/ directory for a Linux kernel.
+
+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 "$3"
+	fi
+}
+
+set_debarch() {
+	if [ "${KBUILD_DEBARCH:+set}" ]; then
+		debarch="$KBUILD_DEBARCH"
+		return
+	fi
+
+	# Attempt to find the correct Debian architecture
+	case "$UTS_MACHINE" in
+	i386|alpha|m68k|riscv*)
+		debarch="$UTS_MACHINE" ;;
+	x86_64)
+		debarch=amd64 ;;
+	sparc*)
+		debarch=sparc$(if_enabled_echo CONFIG_64BIT 64) ;;
+	s390*)
+		debarch=s390x ;;
+	ppc*)
+		if is_enabled CONFIG_64BIT; then
+			debarch=ppc64$(if_enabled_echo CONFIG_CPU_LITTLE_ENDIAN el)
+		else
+			debarch=powerpc$(if_enabled_echo CONFIG_SPE spe)
+		fi
+		;;
+	parisc*)
+		debarch=hppa ;;
+	mips*)
+		if is_enabled CONFIG_CPU_LITTLE_ENDIAN; then
+			debarch=mips$(if_enabled_echo CONFIG_64BIT 64)$(if_enabled_echo CONFIG_CPU_MIPSR6 r6)el
+		elif is_enabled CONFIG_CPU_MIPSR6; then
+			debarch=mips$(if_enabled_echo CONFIG_64BIT 64)r6
+		else
+			debarch=mips
+		fi
+		;;
+	aarch64|arm64)
+		debarch=arm64 ;;
+	arm*)
+		if is_enabled CONFIG_AEABI; then
+			debarch=arm$(if_enabled_echo CONFIG_VFP hf el)
+		else
+			debarch=arm
+		fi
+		;;
+	openrisc)
+		debarch=or1k ;;
+	sh)
+		if is_enabled CONFIG_CPU_SH3; then
+			debarch=sh3$(if_enabled_echo CONFIG_CPU_BIG_ENDIAN eb)
+		elif is_enabled CONFIG_CPU_SH4; then
+			debarch=sh4$(if_enabled_echo CONFIG_CPU_BIG_ENDIAN eb)
+		fi
+		;;
+	um)
+		if is_enabled CONFIG_64BIT; then
+			debarch=amd64
+		else
+			debarch=i386
+		fi
+		;;
+	loongarch64)
+		debarch=loong64 ;;
+	esac
+	if [ -z "$debarch" ]; then
+		debarch=$(dpkg-architecture -qDEB_HOST_ARCH)
+		echo "" >&2
+		echo "** ** **  WARNING  ** ** **" >&2
+		echo "" >&2
+		echo "Your architecture doesn't have its equivalent" >&2
+		echo "Debian userspace architecture defined!" >&2
+		echo "Falling back to the current host architecture ($debarch)." >&2
+		echo "Please add support for $UTS_MACHINE to ${0} ..." >&2
+		echo "" >&2
+	fi
+}
+
+# Create debian/source/ if it is a source package build
+gen_source ()
+{
+	mkdir -p debian/source
+
+	echo "3.0 (quilt)" > debian/source/format
+
+	{
+		echo "diff-ignore"
+		echo "extend-diff-ignore = .*"
+	} > debian/source/local-options
+
+	# Add .config as a patch
+	mkdir -p debian/patches
+	{
+		echo "Subject: Add .config"
+		echo "Author: ${maintainer}"
+		echo
+		echo "--- /dev/null"
+		echo "+++ linux/.config"
+		diff -u /dev/null "${KCONFIG_CONFIG}" | tail -n +3
+	} > debian/patches/config.patch
+	echo config.patch > debian/patches/series
+
+	"${srctree}/scripts/package/gen-diff-patch" debian/patches/diff.patch
+	if [ -s debian/patches/diff.patch ]; then
+		sed -i "
+			1iSubject: Add local diff
+			1iAuthor: ${maintainer}
+			1i
+		" debian/patches/diff.patch
+
+		echo diff.patch >> debian/patches/series
+	else
+		rm -f debian/patches/diff.patch
+	fi
+}
+
+rm -rf debian
+mkdir debian
+
+user=${KBUILD_BUILD_USER:-$(id -nu)}
+name=${DEBFULLNAME:-${user}}
+if [ "${DEBEMAIL:+set}" ]; then
+	email=${DEBEMAIL}
+else
+	buildhost=${KBUILD_BUILD_HOST:-$(hostname -f 2>/dev/null || hostname)}
+	email="${user}@${buildhost}"
+fi
+maintainer="${name} <${email}>"
+
+while [ $# -gt 0 ]; do
+	case "$1" in
+	--need-source)
+		gen_source
+		shift
+		;;
+	*)
+		break
+		;;
+	esac
+done
+
+# Some variables and settings used throughout the script
+if [ "${KDEB_PKGVERSION:+set}" ]; then
+	packageversion=$KDEB_PKGVERSION
+else
+	upstream_version=$("${srctree}/scripts/setlocalversion" --no-local "${srctree}" | sed 's/-\(rc[1-9]\)/~\1/')
+	debian_revision=$("${srctree}/scripts/build-version")
+	packageversion=${upstream_version}-${debian_revision}
+fi
+sourcename=${KDEB_SOURCENAME:-linux-upstream}
+
+if [ "$ARCH" = "um" ] ; then
+	packagename=user-mode-linux
+else
+	packagename=linux-image
+fi
+
+debarch=
+set_debarch
+
+# Try to determine distribution
+if [ "${KDEB_CHANGELOG_DIST:+set}" ]; then
+        distribution=$KDEB_CHANGELOG_DIST
+# In some cases lsb_release returns the codename as n/a, which breaks dpkg-parsechangelog
+elif distribution=$(lsb_release -cs 2>/dev/null) && [ -n "$distribution" ] && [ "$distribution" != "n/a" ]; then
+        : # nothing to do in this case
+else
+        distribution="unstable"
+        echo >&2 "Using default distribution of 'unstable' in the changelog"
+        echo >&2 "Install lsb-release or set \$KDEB_CHANGELOG_DIST explicitly"
+fi
+
+echo $debarch > debian/arch
+
+host_gnu=$(dpkg-architecture -a "${debarch}" -q DEB_HOST_GNU_TYPE | sed 's/_/-/g')
+
+# Generate a simple changelog template
+cat <<EOF > debian/changelog
+$sourcename ($packageversion) $distribution; urgency=low
+
+  * Custom built Linux kernel.
+
+ -- $maintainer  $(date -R)
+EOF
+
+# Generate a control file
+cat <<EOF > debian/control
+Source: $sourcename
+Section: kernel
+Priority: optional
+Maintainer: $maintainer
+Rules-Requires-Root: no
+Build-Depends: debhelper-compat (= 12)
+Build-Depends-Arch: bc, bison, flex,
+ gcc-${host_gnu} <!pkg.${sourcename}.nokernelheaders>,
+ kmod, libdw-dev:native, libelf-dev:native,
+ libssl-dev:native, libssl-dev <!pkg.${sourcename}.nokernelheaders>,
+ python3:native, rsync
+Homepage: https://www.kernel.org/
+
+Package: $packagename-${KERNELRELEASE}
+Architecture: $debarch
+Description: Linux kernel, version ${KERNELRELEASE}
+ This package contains the Linux kernel, modules and corresponding other
+ files, version: ${KERNELRELEASE}.
+EOF
+
+if [ "${SRCARCH}" != um ]; then
+cat <<EOF >> debian/control
+
+Package: linux-libc-dev
+Section: devel
+Provides: linux-kernel-headers
+Architecture: $debarch
+Description: Linux support headers for userspace development
+ This package provides userspaces headers from the Linux kernel.  These headers
+ are used by the installed headers for GNU glibc and other system libraries.
+Multi-Arch: same
+EOF
+
+if is_enabled CONFIG_MODULES; then
+cat <<EOF >> debian/control
+
+Package: linux-headers-${KERNELRELEASE}
+Architecture: $debarch
+Build-Profiles: <!pkg.${sourcename}.nokernelheaders>
+Description: Linux kernel headers for ${KERNELRELEASE} on $debarch
+ This package provides kernel header files for ${KERNELRELEASE} on $debarch
+ .
+ This is useful for people who need to build external modules
+EOF
+fi
+fi
+
+if is_enabled CONFIG_DEBUG_INFO; then
+cat <<EOF >> debian/control
+
+Package: linux-image-${KERNELRELEASE}-dbg
+Section: debug
+Architecture: $debarch
+Build-Profiles: <!pkg.${sourcename}.nokerneldbg>
+Description: Linux kernel debugging symbols for ${KERNELRELEASE}
+ This package will come in handy if you need to debug the kernel. It provides
+ all the necessary debug symbols for the kernel and its modules.
+EOF
+fi
+
+cat <<EOF > debian/rules.vars
+ARCH := ${ARCH}
+KERNELRELEASE := ${KERNELRELEASE}
+EOF
+
+cp "${srctree}/scripts/package/debian/copyright" debian/
+cp "${srctree}/scripts/package/debian/rules" debian/
+
+exit 0