php-fpm trying to kill another user's pool results in an infinite loop and 99% cpu usage

Description

Hi,

We've come across an interesting issue where an instance of the php-fpm pool ran by one user gets stuck restarting and tries to kill another user's php-fpm pool instances.. similar issue has been described here:

https://bugs.php.net/bug.php?id=74709

Can you please help us fix this? Here's a snippet of strace of the process in question:-

strace: Process 34545 attached
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)
fcntl(3, F_GETLK, {l_type=F_RDLCK, l_whence=SEEK_SET, l_start=1, l_len=1, l_pid=32328}) = 0
kill(32328, SIGTERM) = -1 EPERM (Operation not permitted)

the process for which above strace is for is owned by user "xyz", while the process it's trying to kill (process id: 32328) is owned by user "anc".

I would also like to add that this causes all of our websites to timeout. by all websites i mean websites which are using the same php version. like for example the process that's currently stuck and reported in my below mssg is using php 8.0.15 and so all of the websites on my server using php 8.0.15 are timing out.

PHP Version

8.0.15

Operating System

CloudLinux v7.9.0 (CentOS 7)

No source file or test is identified. Start by reproducing the php-fpm pool restart on PHP 8.0.15 under CloudLinux v7.9/CentOS 7 and inspect the repeated kill and file-lock sequence shown by strace. Done means an EPERM result cannot cause an infinite loop affecting another user's pool, and sites using the same PHP version remain responsive.