Hi,
in order to further investigate a PHP-FPM lockup:
# strace -y -f -p 56941
Process 56941 attached
fcntl(4</tmp/.ZendSem.* (deleted)>, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=0, len=1}
(gdb) bt
#0 0x00007f10ec1aa084 in fcntl () from /lib64/libc.so.6
#1 0x00007f10e392711a in ?? ()...