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, 236 insertions, 0 deletions

diff --git a/scripts/config b/scripts/config
new file mode 100755
index 000000000..ea475c07d
--- /dev/null
+++ b/scripts/config
@@ -0,0 +1,236 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-2.0
+# Manipulate options in a .config file from the command line
+
+myname=${0##*/}
+
+# If no prefix forced, use the default CONFIG_
+CONFIG_="${CONFIG_-CONFIG_}"
+
+# We use an uncommon delimiter for sed substitutions
+SED_DELIM=$(echo -en "\001")
+
+usage() {
+	cat >&2 <<EOL
+Manipulate options in a .config file from the command line.
+Usage:
+$myname options command ...
+commands:
+	--enable|-e option   Enable option
+	--disable|-d option  Disable option
+	--module|-m option   Turn option into a module
+	--set-str option string
+	                     Set option to "string"
+	--set-val option value
+	                     Set option to value
+	--undefine|-u option Undefine option
+	--state|-s option    Print state of option (n,y,m,undef)
+
+	--enable-after|-E beforeopt option
+                             Enable option directly after other option
+	--disable-after|-D beforeopt option
+                             Disable option directly after other option
+	--module-after|-M beforeopt option
+                             Turn option into module directly after other option
+	--refresh            Refresh the config using old settings
+
+	commands can be repeated multiple times
+
+options:
+	--file config-file   .config file to change (default .config)
+	--keep-case|-k       Keep next symbols' case (dont' upper-case it)
+
+$myname doesn't check the validity of the .config file. This is done at next
+make time.
+
+By default, $myname will upper-case the given symbol. Use --keep-case to keep
+the case of all following symbols unchanged.
+
+$myname uses 'CONFIG_' as the default symbol prefix. Set the environment
+variable CONFIG_ to the prefix to use. Eg.: CONFIG_="FOO_" $myname ...
+EOL
+	exit 1
+}
+
+checkarg() {
+	ARG="$1"
+	if [ "$ARG" = "" ] ; then
+		usage
+	fi
+	case "$ARG" in
+	${CONFIG_}*)
+		ARG="${ARG/${CONFIG_}/}"
+		;;
+	esac
+	if [ "$MUNGE_CASE" = "yes" ] ; then
+		ARG="`echo $ARG | tr a-z A-Z`"
+	fi
+}
+
+txt_append() {
+	local anchor="$1"
+	local insert="$2"
+	local infile="$3"
+	local tmpfile="$infile.swp"
+
+	# sed append cmd: 'a\' + newline + text + newline
+	cmd="$(printf "a\\%b$insert" "\n")"
+
+	sed -e "/$anchor/$cmd" "$infile" >"$tmpfile"
+	# replace original file with the edited one
+	mv "$tmpfile" "$infile"
+}
+
+txt_subst() {
+	local before="$1"
+	local after="$2"
+	local infile="$3"
+	local tmpfile="$infile.swp"
+
+	sed -e "s$SED_DELIM$before$SED_DELIM$after$SED_DELIM" "$infile" >"$tmpfile"
+	# replace original file with the edited one
+	mv "$tmpfile" "$infile"
+}
+
+txt_delete() {
+	local text="$1"
+	local infile="$2"
+	local tmpfile="$infile.swp"
+
+	sed -e "/$text/d" "$infile" >"$tmpfile"
+	# replace original file with the edited one
+	mv "$tmpfile" "$infile"
+}
+
+set_var() {
+	local name=$1 new=$2 before=$3
+
+	name_re="^($name=|# $name is not set)"
+	before_re="^($before=|# $before is not set)"
+	if test -n "$before" && grep -Eq "$before_re" "$FN"; then
+		txt_append "^$before=" "$new" "$FN"
+		txt_append "^# $before is not set" "$new" "$FN"
+	elif grep -Eq "$name_re" "$FN"; then
+		txt_subst "^$name=.*" "$new" "$FN"
+		txt_subst "^# $name is not set" "$new" "$FN"
+	else
+		echo "$new" >>"$FN"
+	fi
+}
+
+undef_var() {
+	local name=$1
+
+	txt_delete "^$name=" "$FN"
+	txt_delete "^# $name is not set" "$FN"
+}
+
+FN=.config
+CMDS=()
+while [[ $# -gt 0 ]]; do
+	if [ "$1" = "--file" ]; then
+		if [ "$2" = "" ]; then
+			usage
+		fi
+		FN="$2"
+		shift 2
+	else
+		CMDS+=("$1")
+		shift
+	fi
+done
+
+set -- "${CMDS[@]}"
+if [ "$1" = "" ] ; then
+	usage
+fi
+
+MUNGE_CASE=yes
+while [ "$1" != "" ] ; do
+	CMD="$1"
+	shift
+	case "$CMD" in
+	--keep-case|-k)
+		MUNGE_CASE=no
+		continue
+		;;
+	--refresh)
+		;;
+	--*-after|-E|-D|-M)
+		checkarg "$1"
+		A=$ARG
+		checkarg "$2"
+		B=$ARG
+		shift 2
+		;;
+	-*)
+		checkarg "$1"
+		shift
+		;;
+	esac
+	case "$CMD" in
+	--enable|-e)
+		set_var "${CONFIG_}$ARG" "${CONFIG_}$ARG=y"
+		;;
+
+	--disable|-d)
+		set_var "${CONFIG_}$ARG" "# ${CONFIG_}$ARG is not set"
+		;;
+
+	--module|-m)
+		set_var "${CONFIG_}$ARG" "${CONFIG_}$ARG=m"
+		;;
+
+	--set-str)
+		# sed swallows one level of escaping, so we need double-escaping
+		set_var "${CONFIG_}$ARG" "${CONFIG_}$ARG=\"${1//\"/\\\\\"}\""
+		shift
+		;;
+
+	--set-val)
+		set_var "${CONFIG_}$ARG" "${CONFIG_}$ARG=$1"
+		shift
+		;;
+	--undefine|-u)
+		undef_var "${CONFIG_}$ARG"
+		;;
+
+	--state|-s)
+		if grep -q "# ${CONFIG_}$ARG is not set" $FN ; then
+			echo n
+		else
+			V="$(grep "^${CONFIG_}$ARG=" $FN)"
+			if [ $? != 0 ] ; then
+				echo undef
+			else
+				V="${V/#${CONFIG_}$ARG=/}"
+				V="${V/#\"/}"
+				V="${V/%\"/}"
+				V="${V//\\\"/\"}"
+				echo "${V}"
+			fi
+		fi
+		;;
+
+	--enable-after|-E)
+		set_var "${CONFIG_}$B" "${CONFIG_}$B=y" "${CONFIG_}$A"
+		;;
+
+	--disable-after|-D)
+		set_var "${CONFIG_}$B" "# ${CONFIG_}$B is not set" "${CONFIG_}$A"
+		;;
+
+	--module-after|-M)
+		set_var "${CONFIG_}$B" "${CONFIG_}$B=m" "${CONFIG_}$A"
+		;;
+
+	--refresh)
+		yes "" | make oldconfig KCONFIG_CONFIG=$FN
+		;;
+
+	*)
+		echo "bad command: $CMD" >&2
+		usage
+		;;
+	esac
+done