install(1) with option "-d" creates directories. If the final target or an intermediate directory is a symbolic link, that points to a none existing file/directory, then install will enter an endless loop.

I believe the behaviour was introduced with
base r272026 | mjg | 2014-09-23 13:41:09 +0200 (Tue, 23 Sep 2014).

It was observed when using mergemaster for a jail setup with ezjail. In that case symlinks visited from host can point to not existing directories on host system.

environment: 
FreeBSD 11.0-CURRENT #10 r292982M:

how to repeat:
% ln -s /notexists /tmp/
% install -d /tmp/notexists &
[1] 9843
% ps -v -p 9843
 PID STAT    TIME  SL RE PAGEIN  VSZ  RSS LIM TSIZ  %CPU %MEM COMMAND
9843 R    1:12.80 127 73      0 8356 2024   -   28 100.0  0.0 install -d /tmp/notexists
% kill -ABRT 9843
% gdb /usr/bin/install install.core
(gdb) bt
#0  stat () at stat.S:3
#1  0x0000000000402e0b in main (argc=<value optimized out>, argv=<value optimized out>) at /usr/src11/usr.bin/xinstall/xinstall.c:1269
(gdb) list 1269
1264            for (p = path;; ++p)
1265                    if (!*p || (p != path && *p  == '/')) {
1266                            ch = *p;
1267                            *p = '\0';
1268    again:
1269                            if (stat(path, &sb) < 0) {
1270                                    if (errno != ENOENT)
1271                                            err(EX_OSERR, "stat %s", path);
1272                                    if (mkdir(path, 0755) < 0) {
1273                                            if (errno == EEXIST)
(gdb) q

The stat call returns ENOENT and mkdir returns with EEXIST - that creates an endless loop.