opcache + MPM ITK might cause apache2 to hang

Description

This is referring to the bug that is present since at least 5.6. It still happens in 7.4 (just confirmed) and the same code is present in 8.x so I assume the behaviour is the same there, too.

Apache + PHP + MPM_ITK hangs at random intervals spamming "Cannot kill process" in the apache error log.

The original bug report is here: https://bugs.php.net/bug.php?id=76482

The fix looks pretty trivial (break the loop when kill fails) but I'm not sure if it would cause other problems.

Quoting the bug history:

It was reported in 5.6.36 but the bug is in 7.1 (reproduced here) and by looking into source code also in current 7.3 branch.

Not only mpm itk is affected but any MPM which switches child processes to different UIDs (via setuid()). Other example is mod_ruid2 - https://github.com/mind04/mod-ruid2/issues/17

kill_all_lockers() has a loop which never ends if killing fails
as kill(mem_usage_check->l_pid, SIGKILL) returns EPERM in errno.

There is

                if (!success) {
                        /* errno is not ESRCH or we ran out of tries to kill the locker */
                        ZCSG(force_restart_time) = time(NULL); /* restore forced restart request */
                        /* cannot kill the locker, bail out with error */
                        zend_accel_error(ACCEL_LOG_ERROR, "Cannot kill process %d: %s!", mem_usage_check->l_pid, strerror(errno));
                }

but it doesn't break the loop. Is brake missing here?

PHP Version

PHP 7.4

Operating System

Debian 11

Start with the opcache kill_all_lockers() implementation and the failure path that logs "Cannot kill process" when kill() returns EPERM. Reproduce the Apache MPM ITK hang if possible, then verify that the failure exits the loop without regressing forced-restart handling.