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, 368 insertions, 0 deletions

diff --git a/scripts/decode_stacktrace.sh b/scripts/decode_stacktrace.sh
new file mode 100755
index 000000000..39d60d477
--- /dev/null
+++ b/scripts/decode_stacktrace.sh
@@ -0,0 +1,368 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-2.0
+# (c) 2014, Sasha Levin <sasha.levin@oracle.com>
+#set -x
+
+usage() {
+	echo "Usage:"
+	echo "	$0 [-R] -r <release>"
+	echo "	$0 [-R] [<vmlinux> [<base_path>|auto [<modules_path>]]]"
+	echo "	$0 -h"
+	echo "Options:"
+	echo "  -R: decode return address instead of caller address."
+}
+
+# Try to find a Rust demangler
+if type llvm-cxxfilt >/dev/null 2>&1 ; then
+	cppfilt=llvm-cxxfilt
+elif type c++filt >/dev/null 2>&1 ; then
+	cppfilt=c++filt
+	cppfilt_opts=-i
+fi
+
+UTIL_SUFFIX=
+if [[ -z ${LLVM:-} ]]; then
+	UTIL_PREFIX=${CROSS_COMPILE:-}
+else
+	UTIL_PREFIX=llvm-
+	if [[ ${LLVM} == */ ]]; then
+		UTIL_PREFIX=${LLVM}${UTIL_PREFIX}
+	elif [[ ${LLVM} == -* ]]; then
+		UTIL_SUFFIX=${LLVM}
+	fi
+fi
+
+READELF=${UTIL_PREFIX}readelf${UTIL_SUFFIX}
+ADDR2LINE=${UTIL_PREFIX}addr2line${UTIL_SUFFIX}
+NM=${UTIL_PREFIX}nm${UTIL_SUFFIX}
+decode_retaddr=false
+
+if [[ $1 == "-h" ]] ; then
+	usage
+	exit 0
+elif [[ $1 == "-R" ]] ; then
+	decode_retaddr=true
+	shift 1
+fi
+
+if [[ $1 == "-r" ]] ; then
+	vmlinux=""
+	basepath="auto"
+	modpath=""
+	release=$2
+
+	for fn in {,/usr/lib/debug}/boot/vmlinux-$release{,.debug} /lib/modules/$release{,/build}/vmlinux ; do
+		if [ -e "$fn" ] ; then
+			vmlinux=$fn
+			break
+		fi
+	done
+
+	if [[ $vmlinux == "" ]] ; then
+		echo "ERROR! vmlinux image for release $release is not found" >&2
+		usage
+		exit 2
+	fi
+else
+	vmlinux=$1
+	basepath=${2-auto}
+	modpath=$3
+	release=""
+	debuginfod=
+
+	# Can we use debuginfod-find?
+	if type debuginfod-find >/dev/null 2>&1 ; then
+		debuginfod=${1-only}
+	fi
+
+	if [[ $vmlinux == "" && -z $debuginfod ]] ; then
+		echo "ERROR! vmlinux image must be specified" >&2
+		usage
+		exit 1
+	fi
+fi
+
+declare aarray_support=true
+declare -A cache 2>/dev/null
+if [[ $? != 0 ]]; then
+	aarray_support=false
+else
+	declare -A modcache
+fi
+
+find_module() {
+	if [[ -n $debuginfod ]] ; then
+		if [[ -n $modbuildid ]] ; then
+			debuginfod-find debuginfo $modbuildid && return
+		fi
+
+		# Only using debuginfod so don't try to find vmlinux module path
+		if [[ $debuginfod == "only" ]] ; then
+			return
+		fi
+	fi
+
+	if [ -z $release ] ; then
+		release=$(gdb -ex 'print init_uts_ns.name.release' -ex 'quit' -quiet -batch "$vmlinux" 2>/dev/null | sed -n 's/\$1 = "\(.*\)".*/\1/p')
+	fi
+	if [ -n "${release}" ] ; then
+		release_dirs="/usr/lib/debug/lib/modules/$release /lib/modules/$release"
+	fi
+
+	found_without_debug_info=false
+	for dir in "$modpath" "$(dirname "$vmlinux")" ${release_dirs}; do
+		if [ -n "${dir}" ] && [ -e "${dir}" ]; then
+			for fn in $(find "$dir" -name "${module//_/[-_]}.ko*") ; do
+				if ${READELF} -WS "$fn" | grep -qwF .debug_line ; then
+					echo $fn
+					return
+				fi
+				found_without_debug_info=true
+			done
+		fi
+	done
+
+	if [[ ${found_without_debug_info} == true ]]; then
+		echo "WARNING! No debugging info in module ${module}, rebuild with DEBUG_KERNEL and DEBUG_INFO" >&2
+	else
+		echo "WARNING! Cannot find .ko for module ${module}, please pass a valid module path" >&2
+	fi
+
+	return 1
+}
+
+parse_symbol() {
+	# The structure of symbol at this point is:
+	#   ([name]+[offset]/[total length])
+	#
+	# For example:
+	#   do_basic_setup+0x9c/0xbf
+
+	if [[ $module == "" ]] ; then
+		local objfile=$vmlinux
+	elif [[ $aarray_support == true && "${modcache[$module]+isset}" == "isset" ]]; then
+		local objfile=${modcache[$module]}
+	else
+		local objfile=$(find_module)
+		if [[ $objfile == "" ]] ; then
+			return
+		fi
+		if [[ $aarray_support == true ]]; then
+			modcache[$module]=$objfile
+		fi
+	fi
+
+	# Remove the englobing parenthesis
+	symbol=${symbol#\(}
+	symbol=${symbol%\)}
+
+	# Strip segment
+	local segment
+	if [[ $symbol == *:* ]] ; then
+		segment=${symbol%%:*}:
+		symbol=${symbol#*:}
+	fi
+
+	# Strip the symbol name so that we could look it up
+	local name=${symbol%+*}
+
+	# Use 'nm vmlinux' to figure out the base address of said symbol.
+	# It's actually faster to call it every time than to load it
+	# all into bash.
+	if [[ $aarray_support == true && "${cache[$module,$name]+isset}" == "isset" ]]; then
+		local base_addr=${cache[$module,$name]}
+	else
+		local base_addr=$(${NM} "$objfile" 2>/dev/null | awk '$3 == "'$name'" && ($2 == "t" || $2 == "T") {print $1; exit}')
+		if [[ $base_addr == "" ]] ; then
+			# address not found
+			return
+		fi
+		if [[ $aarray_support == true ]]; then
+			cache[$module,$name]="$base_addr"
+		fi
+	fi
+	# Let's start doing the math to get the exact address into the
+	# symbol. First, strip out the symbol total length.
+	local expr=${symbol%/*}
+	# Also parse the offset from symbol.
+	local offset=${expr#*+}
+	offset=$((offset))
+
+	# Now, replace the symbol name with the base address we found
+	# before.
+	expr=${expr/$name/0x$base_addr}
+
+	# Evaluate it to find the actual address
+	# The stack trace shows the return address, which is the next
+	# instruction after the actual call, so as long as it's in the same
+	# symbol, subtract one from that to point the call instruction.
+	if [[ $decode_retaddr == false && $offset != 0 ]]; then
+		expr=$((expr-1))
+	else
+		expr=$((expr))
+	fi
+	local address=$(printf "%x\n" "$expr")
+
+	# Pass it to addr2line to get filename and line number
+	# Could get more than one result
+	if [[ $aarray_support == true && "${cache[$module,$address]+isset}" == "isset" ]]; then
+		local code=${cache[$module,$address]}
+	else
+		local code=$(${ADDR2LINE} -i -e "$objfile" "$address" 2>/dev/null)
+		if [[ $aarray_support == true ]]; then
+			cache[$module,$address]=$code
+		fi
+	fi
+
+	# addr2line doesn't return a proper error code if it fails, so
+	# we detect it using the value it prints so that we could preserve
+	# the offset/size into the function and bail out
+	if [[ $code == "??:0" ]]; then
+		return
+	fi
+
+	# Strip out the base of the path on each line
+	code=$(while read -r line; do echo "${line#$basepath/}"; done <<< "$code")
+
+	# In the case of inlines, move everything to same line
+	code=${code//$'\n'/' '}
+
+	# Demangle if the name looks like a Rust symbol and if
+	# we got a Rust demangler
+	if [[ $name =~ ^_R && $cppfilt != "" ]] ; then
+		name=$("$cppfilt" "$cppfilt_opts" "$name")
+	fi
+
+	# Replace old address with pretty line numbers
+	symbol="$segment$name ($code)"
+}
+
+debuginfod_get_vmlinux() {
+	local vmlinux_buildid=${1##* }
+
+	if [[ $vmlinux != "" ]]; then
+		return
+	fi
+
+	if [[ $vmlinux_buildid =~ ^[0-9a-f]+ ]]; then
+		vmlinux=$(debuginfod-find debuginfo $vmlinux_buildid)
+		if [[ $? -ne 0 ]] ; then
+			echo "ERROR! vmlinux image not found via debuginfod-find" >&2
+			usage
+			exit 2
+		fi
+		return
+	fi
+	echo "ERROR! Build ID for vmlinux not found. Try passing -r or specifying vmlinux" >&2
+	usage
+	exit 2
+}
+
+decode_code() {
+	local scripts=`dirname "${BASH_SOURCE[0]}"`
+	local lim="Code: "
+
+	echo -n "${1%%${lim}*}"
+	echo "${lim}${1##*${lim}}" | $scripts/decodecode
+}
+
+handle_line() {
+	if [[ $basepath == "auto" && $vmlinux != "" ]] ; then
+		module=""
+		symbol="kernel_init+0x0/0x0"
+		parse_symbol
+		basepath=${symbol#kernel_init (}
+		basepath=${basepath%/init/main.c:*)}
+	fi
+
+	local words spaces
+
+	# Tokenize: words and spaces to preserve the alignment
+	read -ra words <<<"$1"
+	IFS='#' read -ra spaces <<<"$(shopt -s extglob; echo "${1//+([^[:space:]])/#}")"
+
+	# Remove hex numbers. Do it ourselves until it happens in the
+	# kernel
+
+	# We need to know the index of the last element before we
+	# remove elements because arrays are sparse
+	local last=$(( ${#words[@]} - 1 ))
+
+	for i in "${!words[@]}"; do
+		# Remove the address
+		if [[ ${words[$i]} =~ \[\<([^]]+)\>\] ]]; then
+			unset words[$i] spaces[$i]
+		fi
+	done
+
+	# Extract info after the symbol if present. E.g.:
+	# func_name+0x54/0x80 (P)
+	#                     ^^^
+	# The regex assumes only uppercase letters will be used. To be
+	# extended if needed.
+	local info_str=""
+	if [[ ${words[$last]} =~ \([A-Z]*\) ]]; then
+		info_str=${words[$last]}
+		unset words[$last] spaces[$last]
+		last=$(( $last - 1 ))
+	fi
+
+	# Join module name with its build id if present, as these were
+	# split during tokenization (e.g. "[module" and "modbuildid]").
+	if [[ ${words[$last]} =~ ^[0-9a-f]+\] ]]; then
+		words[$last-1]="${words[$last-1]} ${words[$last]}"
+		unset words[$last] spaces[$last]
+		last=$(( $last - 1 ))
+	fi
+
+	if [[ ${words[$last]} =~ \[([^]]+)\] ]]; then
+		module=${words[$last]}
+		# some traces format is "(%pS)", which like "(foo+0x0/0x1 [bar])"
+		# so $module may like "[bar])". Strip the right parenthesis firstly
+		module=${module%\)}
+		module=${module#\[}
+		module=${module%\]}
+		modbuildid=${module#* }
+		module=${module% *}
+		if [[ $modbuildid == $module ]]; then
+			modbuildid=
+		fi
+		symbol=${words[$last-1]}
+		unset words[$last-1] spaces[$last-1]
+	else
+		# The symbol is the last element, process it
+		symbol=${words[$last]}
+		module=
+		modbuildid=
+	fi
+
+	unset words[$last]
+	parse_symbol # modifies $symbol
+
+	# Add up the line number to the symbol
+	for i in "${!words[@]}"; do
+		echo -n "${spaces[i]}${words[i]}"
+	done
+	echo "${spaces[$last]}${symbol}${module:+ ${module}}${info_str:+ ${info_str}}"
+}
+
+while read line; do
+	# Strip unexpected carriage return at end of line
+	line=${line%$'\r'}
+
+	# Let's see if we have an address in the line
+	if [[ $line =~ \[\<([^]]+)\>\] ]] ||
+	   [[ $line =~ [^+\ ]+\+0x[0-9a-f]+/0x[0-9a-f]+ ]]; then
+		# Translate address to line numbers
+		handle_line "$line"
+	# Is it a code line?
+	elif [[ $line == *Code:* ]]; then
+		decode_code "$line"
+	# Is it a version line?
+	elif [[ -n $debuginfod && $line =~ PID:\ [0-9]+\ Comm: ]]; then
+		debuginfod_get_vmlinux "$line"
+	else
+		# Nothing special in this line, show it as is
+		echo "$line"
+	fi
+done