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, 212 insertions, 0 deletions

diff --git a/scripts/setlocalversion b/scripts/setlocalversion
new file mode 100755
index 000000000..28169d7e1
--- /dev/null
+++ b/scripts/setlocalversion
@@ -0,0 +1,212 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# This scripts adds local version information from the version
+# control system git.
+#
+# If something goes wrong, send a mail the kernel build mailinglist
+# (see MAINTAINERS) and CC Nico Schottelius
+# <nico-linuxsetlocalversion -at- schottelius.org>.
+#
+#
+
+set -e
+
+usage() {
+	echo "Usage: $0 [--no-local] [srctree]" >&2
+	exit 1
+}
+
+no_local=false
+if test "$1" = "--no-local"; then
+	no_local=true
+	shift
+fi
+
+srctree=.
+if test $# -gt 0; then
+	srctree=$1
+	shift
+fi
+if test $# -gt 0 -o ! -d "$srctree"; then
+	usage
+fi
+
+try_tag() {
+	tag="$1"
+
+	# Is $tag an annotated tag?
+	if [ "$(git cat-file -t "$tag" 2> /dev/null)" != tag ]; then
+		 return
+	fi
+
+	# Is it an ancestor of HEAD, and if so, how many commits are in $tag..HEAD?
+	# shellcheck disable=SC2046 # word splitting is the point here
+	set -- $(git rev-list --count --left-right "$tag"...HEAD 2> /dev/null)
+
+	# $1 is 0 if and only if $tag is an ancestor of HEAD. Use
+	# string comparison, because $1 is empty if the 'git rev-list'
+	# command somehow failed.
+	if [ "$1" != 0 ]; then
+		return
+	fi
+
+	# $2 is the number of commits in the range $tag..HEAD, possibly 0.
+	count="$2"
+}
+
+scm_version()
+{
+	local short=false
+	local no_dirty=false
+	local tag
+
+	while [ $# -gt 0 ];
+	do
+		case "$1" in
+		--short)
+			short=true;;
+		--no-dirty)
+			no_dirty=true;;
+		esac
+		shift
+	done
+
+	cd "$srctree"
+
+	if test -n "$(git rev-parse --show-cdup 2>/dev/null)"; then
+		return
+	fi
+
+	if ! head=$(git rev-parse --verify HEAD 2>/dev/null); then
+		return
+	fi
+
+	# mainline kernel:  6.2.0-rc5  ->  v6.2-rc5
+	# stable kernel:    6.1.7      ->  v6.1.7
+	version_tag=v$(echo "${KERNELVERSION}" | sed -E 's/^([0-9]+\.[0-9]+)\.0(.*)$/\1\2/')
+
+	# try_tag initializes count if the tag is usable.
+	count=
+
+	# If a localversion* file exists, and the corresponding
+	# annotated tag exists and is an ancestor of HEAD, use
+	# it. This is the case in linux-next.
+	if [ -n "${file_localversion#-}" ] ; then
+		try_tag "${file_localversion#-}"
+	fi
+
+	# Otherwise, if a localversion* file exists, and the tag
+	# obtained by appending it to the tag derived from
+	# KERNELVERSION exists and is an ancestor of HEAD, use
+	# it. This is e.g. the case in linux-rt.
+	if [ -z "${count}" ] && [ -n "${file_localversion}" ]; then
+		try_tag "${version_tag}${file_localversion}"
+	fi
+
+	# Otherwise, default to the annotated tag derived from KERNELVERSION.
+	if [ -z "${count}" ]; then
+		try_tag "${version_tag}"
+	fi
+
+	# If we are at the tagged commit, we ignore it because the
+	# version is well-defined. If none of the attempted tags exist
+	# or were usable, $count is still empty.
+	if [ -z "${count}" ] || [ "${count}" -gt 0 ]; then
+
+		# If only the short version is requested, don't bother
+		# running further git commands
+		if $short; then
+			echo "+"
+			return
+		fi
+
+		# If we are past the tagged commit, we pretty print it.
+		# (like 6.1.0-14595-g292a089d78d3)
+		if [ -n "${count}" ]; then
+			printf "%s%05d" "-" "${count}"
+		fi
+
+		# Add -g and exactly 12 hex chars.
+		printf '%s%.12s' -g "$head"
+	fi
+
+	if ${no_dirty}; then
+		return
+	fi
+
+	# Check for uncommitted changes.
+	# This script must avoid any write attempt to the source tree, which
+	# might be read-only.
+	# You cannot use 'git describe --dirty' because it tries to create
+	# .git/index.lock .
+	# First, with git-status, but --no-optional-locks is only supported in
+	# git >= 2.14, so fall back to git-diff-index if it fails. Note that
+	# git-diff-index does not refresh the index, so it may give misleading
+	# results.
+	# See git-update-index(1), git-diff-index(1), and git-status(1).
+	if {
+		git --no-optional-locks status -uno --porcelain 2>/dev/null ||
+		git diff-index --name-only HEAD
+	} | read dummy; then
+		printf '%s' -dirty
+	fi
+}
+
+collect_files()
+{
+	local file res=
+
+	for file; do
+		case "$file" in
+		*\~*)
+			continue
+			;;
+		esac
+		if test -e "$file"; then
+			res="$res$(cat "$file")"
+		fi
+	done
+	echo "$res"
+}
+
+if [ -z "${KERNELVERSION}" ]; then
+	echo "KERNELVERSION is not set" >&2
+	exit 1
+fi
+
+# localversion* files in the build and source directory
+file_localversion="$(collect_files localversion*)"
+if test ! "$srctree" -ef .; then
+	file_localversion="${file_localversion}$(collect_files "$srctree"/localversion*)"
+fi
+
+if ${no_local}; then
+	echo "${KERNELVERSION}$(scm_version --no-dirty)"
+	exit 0
+fi
+
+if ! test -e include/config/auto.conf; then
+	echo "Error: kernelrelease not valid - run 'make prepare' to update it" >&2
+	exit 1
+fi
+
+# version string from CONFIG_LOCALVERSION
+config_localversion=$(sed -n 's/^CONFIG_LOCALVERSION=\(.*\)$/\1/p' include/config/auto.conf)
+
+# scm version string if not at the kernel version tag or at the file_localversion
+if grep -q "^CONFIG_LOCALVERSION_AUTO=y$" include/config/auto.conf; then
+	# full scm version string
+	scm_version="$(scm_version)"
+elif [ "${LOCALVERSION+set}" != "set" ]; then
+	# If the variable LOCALVERSION is not set, append a plus
+	# sign if the repository is not in a clean annotated or
+	# signed tagged state (as git describe only looks at signed
+	# or annotated tags - git tag -a/-s).
+	#
+	# If the variable LOCALVERSION is set (including being set
+	# to an empty string), we don't want to append a plus sign.
+	scm_version="$(scm_version --short)"
+fi
+
+echo "${KERNELVERSION}${file_localversion}${config_localversion}${LOCALVERSION}${scm_version}"