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, 286 insertions, 0 deletions

diff --git a/scripts/coccicheck b/scripts/coccicheck
new file mode 100755
index 000000000..8dd766009
--- /dev/null
+++ b/scripts/coccicheck
@@ -0,0 +1,286 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-2.0
+# Linux kernel coccicheck
+#
+# Read Documentation/dev-tools/coccinelle.rst
+#
+# This script requires at least spatch
+# version 1.0.0-rc11.
+
+DIR="$(dirname $(readlink -f $0))/.."
+SPATCH="`which ${SPATCH:=spatch}`"
+
+if [ ! -x "$SPATCH" ]; then
+    echo 'spatch is part of the Coccinelle project and is available at http://coccinelle.lip6.fr/'
+    exit 1
+fi
+
+SPATCH_VERSION=$($SPATCH --version | head -1 | awk '{print $3}')
+
+USE_JOBS="no"
+$SPATCH --help | grep -e "--jobs" > /dev/null && USE_JOBS="yes"
+
+# The verbosity may be set by the environmental parameter V=
+# as for example with 'make V=1 coccicheck'
+
+if [ -n "$V" -a "$V" != "0" ]; then
+	VERBOSE="$V"
+else
+	VERBOSE=0
+fi
+
+FLAGS="--very-quiet"
+
+# You can use SPFLAGS to append extra arguments to coccicheck or override any
+# heuristics done in this file as Coccinelle accepts the last options when
+# options conflict.
+#
+# A good example for use of SPFLAGS is if you want to debug your cocci script,
+# you can for instance use the following:
+#
+# $ export COCCI=scripts/coccinelle/misc/irqf_oneshot.cocci
+# $ make coccicheck MODE=report DEBUG_FILE="all.err" SPFLAGS="--profile --show-trying" M=./drivers/mfd/arizona-irq.c
+#
+# "--show-trying" should show you what rule is being processed as it goes to
+# stdout, you do not need a debug file for that. The profile output will be
+# be sent to stdout, if you provide a DEBUG_FILE the profiling data can be
+# inspected there.
+#
+# --profile will not output if --very-quiet is used, so avoid it.
+echo $SPFLAGS | grep -E -e "--profile|--show-trying" 2>&1 > /dev/null
+if [ $? -eq 0 ]; then
+	FLAGS="--quiet"
+fi
+
+# spatch only allows include directories with the syntax "-I include"
+# while gcc also allows "-Iinclude" and "-include include"
+COCCIINCLUDE=${LINUXINCLUDE//-I/-I }
+COCCIINCLUDE=${COCCIINCLUDE// -include/ --include}
+
+if [ "$C" = "1" -o "$C" = "2" ]; then
+    ONLINE=1
+
+    if [[ $# -le 0 ]]; then
+	    echo ''
+	    echo 'Specifying both the variable "C" and rule "coccicheck" in the make
+command results in a shift count error.'
+	    echo ''
+	    echo 'Try specifying "scripts/coccicheck" as a value for the CHECK variable instead.'
+	    echo ''
+	    echo 'Example:	make C=2 CHECK=scripts/coccicheck drivers/net/ethernet/ethoc.o'
+	    echo ''
+	    exit 1
+    fi
+
+    # Take only the last argument, which is the C file to test
+    shift $(( $# - 1 ))
+    OPTIONS="$COCCIINCLUDE $1"
+
+    # No need to parallelize Coccinelle since this mode takes one input file.
+    NPROC=1
+else
+    ONLINE=0
+    OPTIONS="--dir $srcroot $COCCIINCLUDE"
+
+    # Use only one thread per core by default if hyperthreading is enabled
+    THREADS_PER_CORE=$(LANG=C lscpu | grep "Thread(s) per core: " | tr -cd "[:digit:]")
+    if [ -z "$J" ]; then
+        NPROC=$(getconf _NPROCESSORS_ONLN)
+	if [ $THREADS_PER_CORE -gt 1 -a $NPROC -gt 4 ] ; then
+		NPROC=$((NPROC/2))
+	fi
+    else
+        NPROC="$J"
+    fi
+fi
+
+if [ "$KBUILD_EXTMOD" != "" ] ; then
+    OPTIONS="--patch $srctree $OPTIONS"
+fi
+
+# You can override by using SPFLAGS
+if [ "$USE_JOBS" = "no" ]; then
+	trap kill_running SIGTERM SIGINT
+	declare -a SPATCH_PID
+elif [ "$NPROC" != "1" ]; then
+	# Using 0 should work as well, refer to _SC_NPROCESSORS_ONLN use on
+	# https://github.com/rdicosmo/parmap/blob/master/setcore_stubs.c
+	OPTIONS="$OPTIONS --jobs $NPROC --chunksize 1"
+fi
+
+if [ "$MODE" = "" ] ; then
+    if [ "$ONLINE" = "0" ] ; then
+	echo 'You have not explicitly specified the mode to use. Using default "report" mode.'
+	echo 'Available modes are the following: patch, report, context, org, chain'
+	echo 'You can specify the mode with "make coccicheck MODE=<mode>"'
+	echo 'Note however that some modes are not implemented by some semantic patches.'
+    fi
+    MODE="report"
+fi
+
+if [ "$MODE" = "chain" ] ; then
+    if [ "$ONLINE" = "0" ] ; then
+	echo 'You have selected the "chain" mode.'
+	echo 'All available modes will be tried (in that order): patch, report, context, org'
+    fi
+elif [ "$MODE" = "report" -o "$MODE" = "org" ] ; then
+    FLAGS="--no-show-diff $FLAGS"
+fi
+
+if [ "$ONLINE" = "0" ] ; then
+    echo ''
+    echo 'Please check for false positives in the output before submitting a patch.'
+    echo 'When using "patch" mode, carefully review the patch before submitting it.'
+    echo ''
+fi
+
+run_cmd_parmap() {
+	if [ $VERBOSE -ne 0 ] ; then
+		echo "Running ($NPROC in parallel): $@"
+	fi
+	if [ "$DEBUG_FILE" != "/dev/null" ]; then
+                echo $@>>$DEBUG_FILE
+                $@ 2>>$DEBUG_FILE
+        else
+                echo $@
+                $@ 2>&1
+	fi
+
+	err=$?
+	if [[ $err -ne 0 ]]; then
+		echo "coccicheck failed"
+		exit $err
+	fi
+}
+
+run_cmd_old() {
+	local i
+	if [ $VERBOSE -ne 0 ] ; then
+		echo "Running ($NPROC in parallel): $@"
+	fi
+	for i in $(seq 0 $(( NPROC - 1)) ); do
+		eval "$@ --max $NPROC --index $i &"
+		SPATCH_PID[$i]=$!
+		if [ $VERBOSE -eq 2 ] ; then
+			echo "${SPATCH_PID[$i]} running"
+		fi
+	done
+	wait
+}
+
+run_cmd() {
+	if [ "$USE_JOBS" = "yes" ]; then
+		run_cmd_parmap $@
+	else
+		run_cmd_old $@
+	fi
+}
+
+kill_running() {
+	for i in $(seq 0 $(( NPROC - 1 )) ); do
+		if [ $VERBOSE -eq 2 ] ; then
+			echo "Killing ${SPATCH_PID[$i]}"
+		fi
+		kill ${SPATCH_PID[$i]} 2>/dev/null
+	done
+}
+
+# You can override heuristics with SPFLAGS, these must always go last
+OPTIONS="$OPTIONS $SPFLAGS"
+
+coccinelle () {
+    COCCI="$1"
+
+    OPT=`grep "Options:" $COCCI | cut -d':' -f2`
+    REQ=`grep "Requires:" $COCCI | cut -d':' -f2 | sed "s| ||"`
+    if [ -n "$REQ" ] && ! { echo "$REQ"; echo "$SPATCH_VERSION"; } | sort -CV ; then
+	    echo "Skipping coccinelle SmPL patch: $COCCI"
+	    echo "You have coccinelle:           $SPATCH_VERSION"
+	    echo "This SmPL patch requires:      $REQ"
+	    return
+    fi
+
+#   The option '--parse-cocci' can be used to syntactically check the SmPL files.
+#
+#    $SPATCH -D $MODE $FLAGS -parse_cocci $COCCI $OPT > /dev/null
+
+    if [ $VERBOSE -ne 0 -a $ONLINE -eq 0 ] ; then
+
+	FILE=${COCCI#$srctree/}
+
+	echo "Processing `basename $COCCI`"
+	echo "with option(s) \"$OPT\""
+	echo ''
+	echo 'Message example to submit a patch:'
+
+	sed -ne 's|^///||p' $COCCI
+
+	if [ "$MODE" = "patch" ] ; then
+	    echo ' The semantic patch that makes this change is available'
+	elif [ "$MODE" = "report" ] ; then
+	    echo ' The semantic patch that makes this report is available'
+	elif [ "$MODE" = "context" ] ; then
+	    echo ' The semantic patch that spots this code is available'
+	elif [ "$MODE" = "org" ] ; then
+	    echo ' The semantic patch that makes this Org report is available'
+	else
+	    echo ' The semantic patch that makes this output is available'
+	fi
+	echo " in $FILE."
+	echo ''
+	echo ' More information about semantic patching is available at'
+	echo ' http://coccinelle.lip6.fr/'
+	echo ''
+
+	if [ "`sed -ne 's|^//#||p' $COCCI`" ] ; then
+	    echo 'Semantic patch information:'
+	    sed -ne 's|^//#||p' $COCCI
+	    echo ''
+	fi
+    fi
+
+    if [ "$MODE" = "chain" ] ; then
+	run_cmd $SPATCH -D patch   \
+		$FLAGS --cocci-file $COCCI $OPT $OPTIONS               || \
+	run_cmd $SPATCH -D report  \
+		$FLAGS --cocci-file $COCCI $OPT $OPTIONS --no-show-diff || \
+	run_cmd $SPATCH -D context \
+		$FLAGS --cocci-file $COCCI $OPT $OPTIONS               || \
+	run_cmd $SPATCH -D org     \
+		$FLAGS --cocci-file $COCCI $OPT $OPTIONS --no-show-diff || exit 1
+    elif [ "$MODE" = "rep+ctxt" ] ; then
+	run_cmd $SPATCH -D report  \
+		$FLAGS --cocci-file $COCCI $OPT $OPTIONS --no-show-diff && \
+	run_cmd $SPATCH -D context \
+		$FLAGS --cocci-file $COCCI $OPT $OPTIONS || exit 1
+    else
+	run_cmd $SPATCH -D $MODE   $FLAGS --cocci-file $COCCI $OPT $OPTIONS || exit 1
+    fi
+
+}
+
+if [ "$DEBUG_FILE" = "" ]; then
+    echo 'You have not explicitly specified the debug file to use.'
+    echo 'Using default "/dev/null" as debug file.'
+    echo 'Debug logs will be printed to stdout.'
+    echo 'You can specify the debug file with "make coccicheck DEBUG_FILE=<debug_file>"'
+    echo ''
+    DEBUG_FILE="/dev/null"
+fi
+
+if [ -f $DEBUG_FILE ]; then
+	echo "Debug file $DEBUG_FILE exists, bailing"
+	exit
+fi
+
+if [ "$COCCI" = "" ] ; then
+    for f in `find $srctree/scripts/coccinelle/ -name '*.cocci' -type f | sort`; do
+        if grep -q "virtual[[:space:]]\+$MODE" "$f"; then
+                coccinelle $f
+        else
+                echo "warning: Skipping $f as it does not match mode '$MODE'"
+        fi
+    done
+else
+    coccinelle $COCCI
+fi