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, 245 insertions, 0 deletions

diff --git a/tools/docs/documentation-file-ref-check b/tools/docs/documentation-file-ref-check
new file mode 100755
index 000000000..0cad42f69
--- /dev/null
+++ b/tools/docs/documentation-file-ref-check
@@ -0,0 +1,245 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0
+#
+# Treewide grep for references to files under Documentation, and report
+# non-existing files in stderr.
+
+use warnings;
+use strict;
+use Getopt::Long qw(:config no_auto_abbrev);
+
+# NOTE: only add things here when the file was gone, but the text wants
+# to mention a past documentation file, for example, to give credits for
+# the original work.
+my %false_positives = (
+	"Documentation/scsi/scsi_mid_low_api.rst" => "Documentation/Configure.help",
+	"drivers/vhost/vhost.c" => "Documentation/virtual/lguest/lguest.c",
+);
+
+my $scriptname = $0;
+$scriptname =~ s,tools/docs/([^/]+/),$1,;
+
+# Parse arguments
+my $help = 0;
+my $fix = 0;
+my $warn = 0;
+
+if (! -e ".git") {
+	printf "Warning: can't check if file exists, as this is not a git tree\n";
+	exit 0;
+}
+
+GetOptions(
+	'fix' => \$fix,
+	'warn' => \$warn,
+	'h|help|usage' => \$help,
+);
+
+if ($help != 0) {
+    print "$scriptname [--help] [--fix]\n";
+    exit -1;
+}
+
+# Step 1: find broken references
+print "Finding broken references. This may take a while...  " if ($fix);
+
+my %broken_ref;
+
+my $doc_fix = 0;
+
+open IN, "git grep ':doc:\`' Documentation/|"
+     or die "Failed to run git grep";
+while (<IN>) {
+	next if (!m,^([^:]+):.*\:doc\:\`([^\`]+)\`,);
+	next if (m,sphinx/,);
+
+	my $file = $1;
+	my $d = $1;
+	my $doc_ref = $2;
+
+	my $f = $doc_ref;
+
+	$d =~ s,(.*/).*,$1,;
+	$f =~ s,.*\<([^\>]+)\>,$1,;
+
+	if ($f =~ m,^/,) {
+		$f = "$f.rst";
+		$f =~ s,^/,Documentation/,;
+	} else {
+		$f = "$d$f.rst";
+	}
+
+	next if (grep -e, glob("$f"));
+
+	if ($fix && !$doc_fix) {
+		print STDERR "\nWARNING: Currently, can't fix broken :doc:`` fields\n";
+	}
+	$doc_fix++;
+
+	print STDERR "$file: :doc:`$doc_ref`\n";
+}
+close IN;
+
+open IN, "git grep 'Documentation/'|"
+     or die "Failed to run git grep";
+while (<IN>) {
+	next if (!m/^([^:]+):(.*)/);
+
+	my $f = $1;
+	my $ln = $2;
+
+	# On linux-next, discard the Next/ directory
+	next if ($f =~ m,^Next/,);
+
+	# Makefiles and scripts contain nasty expressions to parse docs
+	next if ($f =~ m/Makefile/ || $f =~ m/\.(sh|py|pl|~|rej|org|orig)$/);
+
+	# It doesn't make sense to parse hidden files
+	next if ($f =~ m#/\.#);
+
+	# Skip this script
+	next if ($f eq $scriptname);
+
+	# Ignore the dir where documentation will be built
+	next if ($ln =~ m,\b(\S*)Documentation/output,);
+
+	if ($ln =~ m,\b(\S*)(Documentation/[A-Za-z0-9\_\.\,\~/\*\[\]\?+-]*)(.*),) {
+		my $prefix = $1;
+		my $ref = $2;
+		my $base = $2;
+		my $extra = $3;
+
+		# some file references are like:
+		# /usr/src/linux/Documentation/DMA-{API,mapping}.txt
+		# For now, ignore them
+		next if ($extra =~ m/^{/);
+
+		# Remove footnotes at the end like:
+		# Documentation/devicetree/dt-object-internal.txt[1]
+		$ref =~ s/(txt|rst)\[\d+]$/$1/;
+
+		# Remove ending ']' without any '['
+		$ref =~ s/\].*// if (!($ref =~ m/\[/));
+
+		# Remove puntuation marks at the end
+		$ref =~ s/[\,\.]+$//;
+
+		my $fulref = "$prefix$ref";
+
+		$fulref =~ s/^(\<file|ref)://;
+		$fulref =~ s/^[\'\`]+//;
+		$fulref =~ s,^\$\(.*\)/,,;
+		$base =~ s,.*/,,;
+
+		# Remove URL false-positives
+		next if ($fulref =~ m/^http/);
+
+		# Remove sched-pelt false-positive
+		next if ($fulref =~ m,^Documentation/scheduler/sched-pelt$,);
+
+		# Discard some build examples from Documentation/target/tcm_mod_builder.rst
+		next if ($fulref =~ m,mnt/sdb/lio-core-2.6.git/Documentation/target,);
+
+		# Check if exists, evaluating wildcards
+		next if (grep -e, glob("$ref $fulref"));
+
+		# Accept relative Documentation patches for tools/
+		if ($f =~ m/tools/) {
+			my $path = $f;
+			$path =~ s,(.*)/.*,$1,;
+			$path =~ s,testing/selftests/bpf,bpf/bpftool,;
+			next if (grep -e, glob("$path/$ref $path/../$ref $path/$fulref"));
+		}
+
+		# Discard known false-positives
+		if (defined($false_positives{$f})) {
+			next if ($false_positives{$f} eq $fulref);
+		}
+
+		if ($fix) {
+			if (!($ref =~ m/(scripts|Kconfig|Kbuild)/)) {
+				$broken_ref{$ref}++;
+			}
+		} elsif ($warn) {
+			print STDERR "Warning: $f references a file that doesn't exist: $fulref\n";
+		} else {
+			print STDERR "$f: $fulref\n";
+		}
+	}
+}
+close IN;
+
+exit 0 if (!$fix);
+
+# Step 2: Seek for file name alternatives
+print "Auto-fixing broken references. Please double-check the results\n";
+
+foreach my $ref (keys %broken_ref) {
+	my $new =$ref;
+
+	my $basedir = ".";
+	# On translations, only seek inside the translations directory
+	$basedir  = $1 if ($ref =~ m,(Documentation/translations/[^/]+),);
+
+	# get just the basename
+	$new =~ s,.*/,,;
+
+	my $f="";
+
+	# usual reason for breakage: DT file moved around
+	if ($ref =~ /devicetree/) {
+		# usual reason for breakage: DT file renamed to .yaml
+		if (!$f) {
+			my $new_ref = $ref;
+			$new_ref =~ s/\.txt$/.yaml/;
+			$f=$new_ref if (-f $new_ref);
+		}
+
+		if (!$f) {
+			my $search = $new;
+			$search =~ s,^.*/,,;
+			$f = qx(find Documentation/devicetree/ -iname "*$search*") if ($search);
+			if (!$f) {
+				# Manufacturer name may have changed
+				$search =~ s/^.*,//;
+				$f = qx(find Documentation/devicetree/ -iname "*$search*") if ($search);
+			}
+		}
+	}
+
+	# usual reason for breakage: file renamed to .rst
+	if (!$f) {
+		$new =~ s/\.txt$/.rst/;
+		$f=qx(find $basedir -iname $new) if ($new);
+	}
+
+	# usual reason for breakage: use dash or underline
+	if (!$f) {
+		$new =~ s/[-_]/[-_]/g;
+		$f=qx(find $basedir -iname $new) if ($new);
+	}
+
+	# Wild guess: seek for the same name on another place
+	if (!$f) {
+		$f = qx(find $basedir -iname $new) if ($new);
+	}
+
+	my @find = split /\s+/, $f;
+
+	if (!$f) {
+		print STDERR "ERROR: Didn't find a replacement for $ref\n";
+	} elsif (scalar(@find) > 1) {
+		print STDERR "WARNING: Won't auto-replace, as found multiple files close to $ref:\n";
+		foreach my $j (@find) {
+			$j =~ s,^./,,;
+			print STDERR "    $j\n";
+		}
+	} else {
+		$f = $find[0];
+		$f =~ s,^./,,;
+		print "INFO: Replacing $ref to $f\n";
+		foreach my $j (qx(git grep -l $ref)) {
+			qx(sed "s\@$ref\@$f\@g" -i $j);
+		}
+	}
+}