From 61b1834c5366c78f0e4d3b21a142d7dd6d6322c1 Mon Sep 17 00:00:00 2001
From: Fabian Vogt <fvogt@suse.de>
Date: Tue, 13 Apr 2021 15:41:00 +0200
Subject: [PATCH] signalblocker: Also block SIGCHLD

The perl-unaware threads created by OpenCV also crash when they encounter a
SIGCHLD signal, which happens by using perl's "system" function for instance.
---
 signalblocker.pm     | 22 +++++++++++-----------
 t/28-signalblocker.t | 14 ++++++++++++--
 2 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/signalblocker.pm b/signalblocker.pm
index 1ff3652c..dea56e12 100644
--- a/signalblocker.pm
+++ b/signalblocker.pm
@@ -1,4 +1,4 @@
-# Copyright © 2020 SUSE LLC
+# Copyright © 2021 SUSE LLC
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -19,23 +19,23 @@ use Mojo::Base -base;
 use bmwqemu;
 use POSIX ':signal_h';
 
-# OpenCV forks a lot of threads and the TERM signal we may get from the
-# parent process would be delivered to an undefined thread. But as those
-# threads do not have a perl interpreter, the perl signal handler (we set
-# later) would crash. So we need to block the TERM signal in the forked
-# processes before we set the signal handler of our choice.
+# OpenCV forks a lot of threads and the signals we may get (TERM from the
+# parent, CHLD from children) would be delivered to an undefined thread.
+# But as those threads do not have a perl interpreter, the perl signal
+# handler would crash. We need to block those signals in those threads, so
+# that they get delivered only to those threads which can handle it.
 
 sub new {
     my ($class, @args) = @_;
 
     # block signals
-    bmwqemu::diag('Blocking SIGTERM');
+    bmwqemu::diag('Blocking SIGCHLD and SIGCHLD');
     my %old_sig = %SIG;
     $SIG{TERM} = 'IGNORE';
     $SIG{INT}  = 'IGNORE';
     $SIG{HUP}  = 'IGNORE';
-    my $sigset = POSIX::SigSet->new(SIGTERM);
-    die "Could not block SIGTERM\n" unless defined sigprocmask(SIG_BLOCK, $sigset, undef);
+    my $sigset = POSIX::SigSet->new(SIGCHLD, SIGTERM);
+    die "Could not block SIGCHLD and SIGTERM\n" unless defined sigprocmask(SIG_BLOCK, $sigset, undef);
 
     # create the actual object holding the information to restore the previous state
     my $self = $class->SUPER::new(@args);
@@ -48,8 +48,8 @@ sub DESTROY {
     my ($self) = @_;
 
     # set back signal handling to default to be able to terminate properly
-    bmwqemu::diag('Unblocking SIGTERM');
-    die "Could not unblock SIGTERM\n" unless defined sigprocmask(SIG_UNBLOCK, $self->{_sigset}, undef);
+    bmwqemu::diag('Unblocking SIGCHLD and SIGTERM');
+    die "Could not unblock SIGCHLD and SIGTERM\n" unless defined sigprocmask(SIG_UNBLOCK, $self->{_sigset}, undef);
     %SIG = %{$self->{_old_sig}};
 }
 
diff --git a/t/28-signalblocker.t b/t/28-signalblocker.t
index 31ddb6f6..9e1a99a5 100755
--- a/t/28-signalblocker.t
+++ b/t/28-signalblocker.t
@@ -1,6 +1,6 @@
 #!/usr/bin/perl
 #
-# Copyright (c) 2020 SUSE LLC
+# Copyright (c) 2021 SUSE LLC
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -44,9 +44,13 @@ my $no_signal_blocker = $ENV{OS_AUTOINST_TEST_NO_SIGNAL_BLOCKER};
 sub thread_count { scalar split("\n", `ps huH p $$`) }
 is(my $last_thread_count = thread_count, 1, 'initially one thread');
 
-# count SIGTERMs we receive; this handler should work after creating/destroying the signal blocker
+# count SIGTERMs we receive; those handlers should work after creating/destroying the signal blocker
+# Note that without these handlers, there won't be any crash in Perl's signal handler as it's never
+# registered for those signals.
 my $received_sigterm = 0;
 $SIG{TERM} = sub { $received_sigterm += 1; note "received SIGTERM $received_sigterm"; };
+my $received_sigchld = 0;
+$SIG{CHLD} = sub { $received_sigchld += 1; note "received SIGCHLD $received_sigchld"; };
 
 # initialize OpenCV via signalblocker and create_threads
 {
@@ -75,6 +79,12 @@ waitpid $fork, 0;
 note 'waiting for at least one signal to be handled' and sleep .2 until $received_sigterm >= 1 || ($timeout -= .2) < 0;
 note "handled $received_sigterm TERM signals";
 ok($received_sigterm > 0, "received SIGTERM $received_sigterm times; no crashes after at least 200 ms idling time");
+
+$received_sigchld = 0;
+# 0 here means WIFEXITED and WEXITSTATUS == 0
+cmp_ok(system("true"), '==', 0, 'system returns exit status');
+is($received_sigchld, 1, 'got SIGCHLD after system');
+
 cmp_ok(thread_count, '<=', $last_thread_count, 'still no new threads after sending signals');
 
 done_testing;
-- 
2.31.1