Description of problem:

Unmounting a DAVFS2 network directory leads to segfault:

# fstab
cat /etc/fstab | grep /media/mundialis_projekte
https://mundialis-alfresco.xxxx.de/alfresco/webdav/projekte /media/mundialis_projekte davfs user,noauto 0 0

# the mounted dir
mount | grep /media/mundialis_projekte
https://mundialis-alfresco.xxxx.de/alfresco/webdav/projekte on /media/mundialis_projekte type fuse (rw,nosuid,nodev,noexec,relatime,user_id=1001,group_id=1001,allow_other,max_read=16384,uid=1001,gid=1001,user=mneteler,helper=davfs)

# trying to unmount it:
umount.davfs /media/mundialis_projekte
Segmentation fault (core dumped)

# version
rpm -qf /usr/sbin/umount.davfs
davfs2-1.5.4-9.fc30.x86_64

# debugging
sudo dnf debuginfo-install davfs2-1.5.4-9.fc30.x86_64

gdb umount.davfs 
GNU gdb (GDB) Fedora 8.3-1.fc30
...
Reading symbols from umount.davfs...
Reading symbols from /usr/lib/debug/usr/sbin/umount.davfs-1.5.4-9.fc30.x86_64.debug...
(gdb) r /media/mundialis_projekte
Starting program: /usr/sbin/umount.davfs /media/mundialis_projekte
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments

Program received signal SIGSEGV, Segmentation fault.
__strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:65
65		VPCMPEQ (%rdi), %ymm0, %ymm1
Missing separate debuginfos, use: dnf debuginfo-install pakchois-0.4-19.fc30.x86_64
(gdb) bt full
#0  __strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:65
No locals.
#1  0x00007ffff7f66588 in count_concat (ap=0x7fffffffced0) at ne_string.c:132
        total = 0
        next = 0x46128800 <error: Cannot access memory at address 0x46128800>
        total = <optimized out>
        next = <optimized out>
#2  ne_concat (str=0x555555556095 "ps -p ") at ne_string.c:179
        ap = {{gp_offset = 16, fp_offset = 0, overflow_arg_area = 0x7fffffffcf50, reg_save_area = 0x7fffffffcef0}}
        total = <optimized out>
        slen = 6
        ret = <optimized out>
#3  0x0000555555555608 in main (argc=<optimized out>, argv=0x7fffffffd098) at umount_davfs.c:163
        short_options = 0x55555555601d "Vhflnrt:v"
        options = {{name = 0x5555555560a0 "version", has_arg = 0, flag = 0x0, val = 86}, {name = 0x5555555560a8 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x0, 
            has_arg = 0, flag = 0x0, val = 0}}
        o = <optimized out>
        mpoint = <optimized out>
        umount_command = 0x0
        m = <optimized out>
        mp = <optimized out>
        pidfile = 0x55555556d6c0 "/var/run/mount.davfs/media-mundialis_projekte.pid"
        pid = 0x46128800 <error: Cannot access memory at address 0x46128800>
        file = 0x555555559260
        ps_command = <optimized out>
        ps_in = <optimized out>
        found = <optimized out>
        n = 140737345544448
        ps_line = 0x7ffff77cff54 <std::ios_base::Init::_S_refcount> "\003"


cat /var/run/mount.davfs/media-mundialis_projekte.pid
9378

uname -a
Linux oboe.mundialis 5.0.14-300.fc30.x86_64 #1 SMP Thu May 9 10:43:38 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

# /proc/cpuinfo
model name	: Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz

I upgraded the machine from F29 to F30 last week, so the DAVFS stuff is identical and worked with F29. 

At time I cannot unmount DAVFS2 directories any more...