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, 194 insertions, 0 deletions

diff --git a/scripts/parse-maintainers.pl b/scripts/parse-maintainers.pl
new file mode 100755
index 000000000..2ca4eb3f1
--- /dev/null
+++ b/scripts/parse-maintainers.pl
@@ -0,0 +1,194 @@
+#!/usr/bin/perl -w
+# SPDX-License-Identifier: GPL-2.0
+
+use strict;
+use Getopt::Long qw(:config no_auto_abbrev);
+
+my $input_file = "MAINTAINERS";
+my $output_file = "MAINTAINERS.new";
+my $output_section = "SECTION.new";
+my $help = 0;
+my $order = 0;
+my $P = $0;
+
+if (!GetOptions(
+		'input=s' => \$input_file,
+		'output=s' => \$output_file,
+		'section=s' => \$output_section,
+		'order!' => \$order,
+		'h|help|usage' => \$help,
+	    )) {
+    die "$P: invalid argument - use --help if necessary\n";
+}
+
+if ($help != 0) {
+    usage();
+    exit 0;
+}
+
+sub usage {
+    print <<EOT;
+usage: $P [options] <pattern matching regexes>
+
+  --input => MAINTAINERS file to read (default: MAINTAINERS)
+  --output => sorted MAINTAINERS file to write (default: MAINTAINERS.new)
+  --section => new sorted MAINTAINERS file to write to (default: SECTION.new)
+  --order => Use the preferred section content output ordering (default: 0)
+    Preferred ordering of section output is:
+      M:  Person acting as a maintainer
+      R:  Person acting as a patch reviewer
+      L:  Mailing list where patches should be sent
+      S:  Maintenance status
+      W:  URI for general information
+      Q:  URI for patchwork tracking
+      B:  URI for bug tracking/submission
+      C:  URI for chat
+      P:  URI or file for subsystem specific coding styles
+      T:  SCM tree type and location
+      F:  File and directory pattern
+      X:  File and directory exclusion pattern
+      N:  File glob
+      K:  Keyword - patch content regex
+
+If <pattern match regexes> exist, then the sections that match the
+regexes are not written to the output file but are written to the
+section file.
+
+EOT
+}
+
+# sort comparison functions
+sub by_category($$) {
+    my ($a, $b) = @_;
+
+    $a = uc $a;
+    $b = uc $b;
+
+    # This always sorts last
+    $a =~ s/THE REST/ZZZZZZ/g;
+    $b =~ s/THE REST/ZZZZZZ/g;
+
+    return $a cmp $b;
+}
+
+sub by_pattern($$) {
+    my ($a, $b) = @_;
+    my $preferred_order = 'MRLSWQBCPTFXNK';
+
+    my $a1 = uc(substr($a, 0, 1));
+    my $b1 = uc(substr($b, 0, 1));
+
+    my $a_index = index($preferred_order, $a1);
+    my $b_index = index($preferred_order, $b1);
+
+    $a_index = 1000 if ($a_index == -1);
+    $b_index = 1000 if ($b_index == -1);
+
+    if (($a1 =~ /^F$/ && $b1 =~ /^F$/) ||
+	($a1 =~ /^X$/ && $b1 =~ /^X$/)) {
+	return $a cmp $b;
+    }
+
+    if ($a_index < $b_index) {
+	return -1;
+    } elsif ($a_index == $b_index) {
+	return 0;
+    } else {
+	return 1;
+    }
+}
+
+sub trim {
+    my $s = shift;
+    $s =~ s/\s+$//;
+    $s =~ s/^\s+//;
+    return $s;
+}
+
+sub alpha_output {
+    my ($hashref, $filename) = (@_);
+
+    return if ! scalar(keys %$hashref);
+
+    open(my $file, '>', "$filename") or die "$P: $filename: open failed - $!\n";
+    my $separator;
+    foreach my $key (sort by_category keys %$hashref) {
+	if ($key eq " ") {
+	    print $file $$hashref{$key};
+	} else {
+	    if (! defined $separator) {
+		$separator = "\n";
+	    } else {
+		print $file $separator;
+	    }
+	    print $file $key . "\n";
+	    if ($order) {
+		foreach my $pattern (sort by_pattern split('\n', %$hashref{$key})) {
+		    print $file ($pattern . "\n");
+		}
+	    } else {
+		foreach my $pattern (split('\n', %$hashref{$key})) {
+		    print $file ($pattern . "\n");
+		}
+	    }
+	}
+    }
+    close($file);
+}
+
+sub file_input {
+    my ($hashref, $filename) = (@_);
+
+    my $lastline = "";
+    my $case = " ";
+    $$hashref{$case} = "";
+
+    open(my $file, '<', "$filename") or die "$P: $filename: open failed - $!\n";
+
+    while (<$file>) {
+        my $line = $_;
+
+        # Pattern line?
+        if ($line =~ m/^([A-Z]):\s*(.*)/) {
+            $line = $1 . ":\t" . trim($2) . "\n";
+            if ($lastline eq "") {
+                $$hashref{$case} = $$hashref{$case} . $line;
+                next;
+            }
+            $case = trim($lastline);
+            exists $$hashref{$case} and die "Header '$case' already exists";
+            $$hashref{$case} = $line;
+            $lastline = "";
+            next;
+        }
+
+        if ($case eq " ") {
+            $$hashref{$case} = $$hashref{$case} . $lastline;
+            $lastline = $line;
+            next;
+        }
+        trim($lastline) eq "" or die ("Odd non-pattern line '$lastline' for '$case'");
+        $lastline = $line;
+    }
+    $$hashref{$case} = $$hashref{$case} . $lastline;
+    close($file);
+}
+
+my %hash;
+my %new_hash;
+
+file_input(\%hash, $input_file);
+
+foreach my $type (@ARGV) {
+    foreach my $key (keys %hash) {
+	if ($key =~ /$type/ || $hash{$key} =~ /$type/) {
+	    $new_hash{$key} = $hash{$key};
+	    delete $hash{$key};
+	}
+    }
+}
+
+alpha_output(\%hash, $output_file);
+alpha_output(\%new_hash, $output_section);
+
+exit(0);