From 761baa2a300e426885675a01e4773193ab7101ff Mon Sep 17 00:00:00 2001
From: Eric Wong <e@yhbt.net>
Date: Mon, 29 Jun 2020 10:34:20 +0000
Subject: spawn: unblock SIGCHLD in subprocess

Subprocess we spawn may want to use SIGCHLD for themselves.
This also ensures we restore default signal handlers
in the pure Perl version.
---
 lib/PublicInbox/Spawn.pm   | 11 ++++++++---
 lib/PublicInbox/SpawnPP.pm |  5 +++++
 t/spawn.t                  | 27 +++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/lib/PublicInbox/Spawn.pm b/lib/PublicInbox/Spawn.pm
index 888283d0..f90d8f6d 100644
--- a/lib/PublicInbox/Spawn.pm
+++ b/lib/PublicInbox/Spawn.pm
@@ -78,7 +78,7 @@ int pi_fork_exec(SV *redirref, SV *file, SV *cmdref, SV *envref, SV *rlimref,
 	const char *filename = SvPV_nolen(file);
 	pid_t pid;
 	char **argv, **envp;
-	sigset_t set, old;
+	sigset_t set, old, cset;
 	int ret, perrnum, cerrnum = 0;
 
 	AV2C_COPY(argv, cmd);
@@ -88,6 +88,10 @@ int pi_fork_exec(SV *redirref, SV *file, SV *cmdref, SV *envref, SV *rlimref,
 	assert(ret == 0 && "BUG calling sigfillset");
 	ret = sigprocmask(SIG_SETMASK, &set, &old);
 	assert(ret == 0 && "BUG calling sigprocmask to block");
+	ret = sigemptyset(&cset);
+	assert(ret == 0 && "BUG calling sigemptyset");
+	ret = sigaddset(&cset, SIGCHLD);
+	assert(ret == 0 && "BUG calling sigaddset for SIGCHLD");
 	pid = vfork();
 	if (pid == 0) {
 		int sig;
@@ -120,9 +124,10 @@ int pi_fork_exec(SV *redirref, SV *file, SV *cmdref, SV *envref, SV *rlimref,
 		}
 
 		/*
-		 * don't bother unblocking, we don't want signals
-		 * to the group taking out a subprocess
+		 * don't bother unblocking other signals for now, just SIGCHLD.
+		 * we don't want signals to the group taking out a subprocess
 		 */
+		(void)sigprocmask(SIG_UNBLOCK, &cset, NULL);
 		execve(filename, argv, envp);
 		exit_err(&cerrnum);
 	}
diff --git a/lib/PublicInbox/SpawnPP.pm b/lib/PublicInbox/SpawnPP.pm
index 34ce2052..a72d5a2d 100644
--- a/lib/PublicInbox/SpawnPP.pm
+++ b/lib/PublicInbox/SpawnPP.pm
@@ -36,6 +36,11 @@ sub pi_fork_exec ($$$$$$) {
 		if ($cd ne '') {
 			chdir $cd or die "chdir $cd: $!";
 		}
+		$SIG{$_} = 'DEFAULT' for keys %SIG;
+		my $cset = POSIX::SigSet->new();
+		$cset->addset(POSIX::SIGCHLD) or die "can't add SIGCHLD: $!";
+		sigprocmask(SIG_UNBLOCK, $cset) or
+					die "can't unblock SIGCHLD: $!";
 		if ($ENV{MOD_PERL}) {
 			exec which('env'), '-i', @$env, @$cmd;
 			die "exec env -i ... $cmd->[0] failed: $!\n";
diff --git a/t/spawn.t b/t/spawn.t
index 44355f43..fd669e22 100644
--- a/t/spawn.t
+++ b/t/spawn.t
@@ -4,6 +4,7 @@ use strict;
 use warnings;
 use Test::More;
 use PublicInbox::Spawn qw(which spawn popen_rd);
+use PublicInbox::Sigfd;
 
 {
 	my $true = which('true');
@@ -17,6 +18,32 @@ use PublicInbox::Spawn qw(which spawn popen_rd);
 	is($?, 0, 'true exited successfully');
 }
 
+{ # ensure waitpid(-1, 0) and SIGCHLD works in spawned process
+	my $script = <<'EOF';
+$| = 1; # unbuffer stdout
+defined(my $pid = fork) or die "fork: $!";
+if ($pid == 0) { exit }
+elsif ($pid > 0) {
+	my $waited = waitpid(-1, 0);
+	$waited == $pid or die "mismatched child $pid != $waited";
+	$? == 0 or die "child err: $>";
+	$SIG{CHLD} = sub { print "HI\n"; exit };
+	print "RDY $$\n";
+	sleep while 1;
+}
+EOF
+	my $oldset = PublicInbox::Sigfd::block_signals();
+	my $rd = popen_rd([$^X, '-e', $script]);
+	diag 'waiting for child to reap grandchild...';
+	chomp(my $line = readline($rd));
+	my ($rdy, $pid) = split(' ', $line);
+	is($rdy, 'RDY', 'got ready signal, waitpid(-1) works in child');
+	ok(kill('CHLD', $pid), 'sent SIGCHLD to child');
+	is(readline($rd), "HI\n", '$SIG{CHLD} works in child');
+	ok(close $rd, 'popen_rd close works');
+	PublicInbox::Sigfd::sig_setmask($oldset);
+}
+
 {
 	my ($r, $w);
 	pipe $r, $w or die "pipe failed: $!";
-- 
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