Bug#1012073: perl: restoring default signal handler may warn with 'SIGTERM handler "DEFAULT" not defined'

[Damyan Ivanov]

Package: perl
Version: 5.34.0-4
Severity: normal

Control: block 923829 by -1

Hi,

While infestigating a random FTBFS in starlet (#923829), it appeared to me that 
the problem is actually in perl. To reproduce te issue, t/12bad_request_line.t 
needs to be run in a loop with the following change:

(starlet packaging repo is at
ssh://git@salsa.debian.org/perl-team/modules/packages/starlet.git)

-------------------------------------------
diff --git a/t/12bad_request_line.t b/t/12bad_request_line.t
index 61b4e7b..bdc8368 100644
--- a/t/12bad_request_line.t
+++ b/t/12bad_request_line.t
@@ -22,7 +22,7 @@ test_tcp(
         my $port = shift;
         local $SIG{__WARN__} = sub {
             ok 0, "No warnings";
-            diag @_;
+            diag Carp::longmess(@_);
         };
         my $loader = Plack::Loader->load('Starlet', port => $port);
         $loader->run(sub { [200, ['Content-Type' => 'text/plain'], ['OK']] });
-------------------------------------------

A sample loop is this:

 while prove -l t/12bad_request_line.t; do date; done

Running this simultaneously in several terminals may help triggering the 
failure.

Eventually it fails with:

#   Failed test 'No warnings'
#   at t/12bad_request_line.t line 24.
# SIGTERM handler "DEFAULT" not defined.
#  at /usr/share/perl5/Parallel/Prefork.pm line 71.
# 	Parallel::Prefork::start(Parallel::Prefork=HASH(0x55cd856355b8)) called at .../lib/Plack/Handler/Starlet.pm line 78
# 	Plack::Handler::Starlet::run(Plack::Handler::Starlet=HASH(0x55cd849b0ad8), CODE(0x55cd8562ac98)) called at t/12bad_request_line.t line 28
# 	main::__ANON__(33415) called at /usr/share/perl5/Test/TCP.pm line 100
# 	Test::TCP::start(Test::TCP=HASH(0x55cd8562aed8)) called at /usr/share/perl5/Test/TCP.pm line 82
# 	Test::TCP::new("Test::TCP", "code", CODE(0x55cd8562aab8)) called at /usr/share/perl5/Test/TCP.pm line 28
# 	Test::TCP::test_tcp("client", CODE(0x55cd854306b0), "server", CODE(0x55cd8562aab8)) called at t/12bad_request_line.t line 31
# Looks like you failed 1 test of 2.
t/12bad_request_line.t .. Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/2 subtests

The lines in Parallel::Prefork where the warning comes from are:
https://salsa.debian.org/perl-team/modules/packages/libparallel-prefork-perl/-/blob/master/lib/Parallel/Prefork.pm#L71

     ...
     68             unless ($pid) {
     69                 # child process
     70                 $self->{in_child} = 1;
     71                 $SIG{$_} = 'DEFAULT' for keys %{$self->trap_signals};
     72                 $SIG{CHLD} = 'DEFAULT'; # revert to original
     73                 exit 0 if $self->signal_received;
     ...

Seems perfectly normal to me - signal handlers are reset in the forked child.

The only plausible source I find is line 3522 of mg.c:
https://salsa.debian.org/perl-team/interpreter/perl/-/blob/debian-5.34/mg.c#L3522

and here my idea of what is going on vanishes. I hope this is enough as a clue.


-- Damyan

-- System Information:
Debian Release: bookworm/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'unstable'), (500, 'stable'), (500, 'oldstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 5.17.0-3-amd64 (SMP w/4 CPU threads; PREEMPT)
Kernel taint flags: TAINT_OOT_MODULE
Locale: LANG=bg_BG.UTF-8, LC_CTYPE=bg_BG.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages perl depends on:
ii  dpkg               1.21.8
ii  libperl5.34        5.34.0-4
ii  perl-base          5.34.0-4
ii  perl-modules-5.34  5.34.0-4

Versions of packages perl recommends:
ii  netbase  6.3

Versions of packages perl suggests:
pn  libtap-harness-archive-perl  <none>
ii  libterm-readline-gnu-perl    1.42-2+b1
ii  libterm-readline-perl-perl   1.0303-2.1
ii  make                         4.3-4.1
ii  perl-doc                     5.34.0-4

-- no debconf information