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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug testsuite/100203] Dejagnu timeouts don't work
Date: Thu, 22 Apr 2021 11:19:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100203

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This seems to be a bug in the Bash 'kill' builtin.

#!/bin/bash

# pass /usr/bin/kill as $1 to use the command not the bash builtin
kill=3D${1:-kill}

sleep 60 &
pid1=3D$!
sleep 60 &
pid2=3D$!

sh -c "exec > /dev/stdout 2>&1 && ($kill -15 -$pid1 $pid2 || { echo kill pg=
rp
failed, trying again... ; $kill -15 $pid1 $pid2 || echo $?;})"
ps -ef | awk 'NR=3D=3D1 || /[s]leep/ {print}'

kill $pid1 $pid2 2>/dev/null


Run without arguments, this script prints something like:

sh: line 0: kill: (-2977556) - No such process
UID          PID    PPID  C STIME TTY          TIME CMD
jwakely  2977556 2977555  0 12:14 pts/2    00:00:00 sleep 60

i.e. the first kill command kills $pid2 but fails to kill -$pid1 (because t=
here
is no such process group) but it exits with status 0, so we don't try again
just $pid1 instead of -$pid1

Passing /usr/bin/kill as $1 to the script we get:

kill: sending signal to -2977547 failed: No such process
kill pgrp failed, trying again...
kill: sending signal to 2977548 failed: No such process
0
UID          PID    PPID  C STIME TTY          TIME CMD

i.e. the first kill command kills $pid2 and fails to kill -$pid1 (as before=
),
but because it was only partial success it exits with non-zero status, and =
we
try again using $pid1 instead of -$pid1. That second command succeeds in
killing $pid1 this time, but gives and error for $pid2 (because it was alre=
ady
killed).

POSIX says:

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/kill.html


    The following exit values shall be returned:

     0
        At least one matching process was found for each pid operand, and t=
he
specified signal was successfully processed for at least one matching proce=
ss.
    >0
        An error occurred.


The Bash builtin seems to be wrong here, because no matching process was fo=
und
for -$pid1 so it should not return 0.=