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, 110 insertions, 0 deletions

diff --git a/scripts/package/buildtar b/scripts/package/buildtar
new file mode 100755
index 000000000..cc87a473c
--- /dev/null
+++ b/scripts/package/buildtar
@@ -0,0 +1,110 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+#
+# buildtar 0.0.5
+#
+# (C) 2004-2006 by Jan-Benedict Glaw <jbglaw@lug-owl.de>
+#
+# This script is used to compile a tarball from the currently
+# prepared kernel. Based upon the builddeb script from
+# Wichert Akkerman <wichert@wiggy.net>.
+#
+
+set -eu
+
+#
+# Some variables and settings used throughout the script
+#
+tmpdir=$1
+
+#
+# Clean-up and re-create the temporary directory
+#
+rm -rf -- "${tmpdir}"
+mkdir -p -- "${tmpdir}/boot"
+
+
+#
+# Try to install dtbs
+#
+if grep -q '^CONFIG_OF_EARLY_FLATTREE=y' include/config/auto.conf; then
+	# Only some architectures with OF support have this target
+	if [ -d "${srctree}/arch/${SRCARCH}/boot/dts" ]; then
+		$MAKE ARCH="${ARCH}" -f ${srctree}/Makefile INSTALL_DTBS_PATH="${tmpdir}/boot/dtbs/${KERNELRELEASE}" dtbs_install
+    fi
+fi
+
+
+#
+# Install modules
+#
+make ARCH="${ARCH}" -f ${srctree}/Makefile INSTALL_MOD_PATH="${tmpdir}" modules_install
+
+
+#
+# Install basic kernel files
+#
+cp -v -- "${objtree}/System.map" "${tmpdir}/boot/System.map-${KERNELRELEASE}"
+cp -v -- "${KCONFIG_CONFIG}" "${tmpdir}/boot/config-${KERNELRELEASE}"
+cp -v -- "${objtree}/vmlinux" "${tmpdir}/boot/vmlinux-${KERNELRELEASE}"
+
+
+#
+# Install arch-specific kernel image(s)
+#
+# Note:
+#   mips and arm64 copy the first image found. This may not produce the desired
+#   outcome because it may pick up a stale file remaining in the build tree.
+#
+case "${ARCH}" in
+	alpha)
+		cp -v -- "${objtree}/arch/alpha/boot/vmlinux.gz" "${tmpdir}/boot/vmlinuz-${KERNELRELEASE}"
+		;;
+	parisc*)
+		cp -v -- "${KBUILD_IMAGE}" "${tmpdir}/boot/vmlinux-${KERNELRELEASE}"
+		[ -f "${objtree}/lifimage" ] && cp -v -- "${objtree}/lifimage" "${tmpdir}/boot/lifimage-${KERNELRELEASE}"
+		;;
+	mips)
+		# Please note the following code may copy a stale file.
+		if [ -f "${objtree}/arch/mips/boot/compressed/vmlinux.bin" ]; then
+			cp -v -- "${objtree}/arch/mips/boot/compressed/vmlinux.bin" "${tmpdir}/boot/vmlinuz-${KERNELRELEASE}"
+		elif [ -f "${objtree}/arch/mips/boot/compressed/vmlinux.ecoff" ]; then
+			cp -v -- "${objtree}/arch/mips/boot/compressed/vmlinux.ecoff" "${tmpdir}/boot/vmlinuz-${KERNELRELEASE}"
+		elif [ -f "${objtree}/arch/mips/boot/compressed/vmlinux.srec" ]; then
+			cp -v -- "${objtree}/arch/mips/boot/compressed/vmlinux.srec" "${tmpdir}/boot/vmlinuz-${KERNELRELEASE}"
+		elif [ -f "${objtree}/vmlinux.32" ]; then
+			cp -v -- "${objtree}/vmlinux.32" "${tmpdir}/boot/vmlinux-${KERNELRELEASE}"
+		elif [ -f "${objtree}/vmlinux.64" ]; then
+			cp -v -- "${objtree}/vmlinux.64" "${tmpdir}/boot/vmlinux-${KERNELRELEASE}"
+		elif [ -f "${objtree}/arch/mips/boot/vmlinux.bin" ]; then
+			cp -v -- "${objtree}/arch/mips/boot/vmlinux.bin" "${tmpdir}/boot/vmlinux-${KERNELRELEASE}"
+		elif [ -f "${objtree}/arch/mips/boot/vmlinux.ecoff" ]; then
+			cp -v -- "${objtree}/arch/mips/boot/vmlinux.ecoff" "${tmpdir}/boot/vmlinux-${KERNELRELEASE}"
+		elif [ -f "${objtree}/arch/mips/boot/vmlinux.srec" ]; then
+			cp -v -- "${objtree}/arch/mips/boot/vmlinux.srec" "${tmpdir}/boot/vmlinux-${KERNELRELEASE}"
+		elif [ -f "${objtree}/vmlinux" ]; then
+			cp -v -- "${objtree}/vmlinux" "${tmpdir}/boot/vmlinux-${KERNELRELEASE}"
+		fi
+		;;
+	arm64)
+		# Please note the following code may copy a stale file.
+		for i in Image.bz2 Image.gz Image.lz4 Image.lzma Image.lzo vmlinuz.efi ; do
+			if [ -f "${objtree}/arch/arm64/boot/${i}" ] ; then
+				cp -v -- "${objtree}/arch/arm64/boot/${i}" "${tmpdir}/boot/vmlinuz-${KERNELRELEASE}"
+				break
+			fi
+		done
+		;;
+	riscv)
+		case "${KBUILD_IMAGE##*/}" in
+			Image.*|vmlinuz.efi)
+				cp -v -- "${KBUILD_IMAGE}" "${tmpdir}/boot/vmlinuz-${KERNELRELEASE}";;
+			*)
+				cp -v -- "${KBUILD_IMAGE}" "${tmpdir}/boot/vmlinux-${KERNELRELEASE}";;
+		esac
+		;;
+	*)
+		cp -v -- "${KBUILD_IMAGE}" "${tmpdir}/boot/vmlinuz-${KERNELRELEASE}"
+		;;
+esac