I recently switched from Kubuntu 17.10 to Kubuntu 18.04 (fresh installed). The problem is the process systemd-udevd is constantly running and consuming 90-100% CPU load. After tinkering around with all devices I found out that it is because of WiFi! Once I turn on WiFi the process starts running and CPU load goes up to 100%. But whenever I turn off the WiFi it gets down to zero!
here is the top results when WiFi is on:

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                           

  338 root      20   0   94336  51744   3120 S  44.7  0.6   0:35.50 systemd-udevd                                                     

  24957 root    20   0   67936  25248   2860 R  40.4  0.3   0:23.85 systemd-udevd                                                     

  328 root      19  -1  150720  53068  52264 S   4.3  0.7   0:07.61 systemd-journal

and running: strace -p 338 makes the following output repeatedly:

strace: Process 338 attached

strace: [ Process PID=338 runs in x32 mode. ]

strace: [ Process PID=338 runs in 64 bit mode. ]

epoll_wait(10, [{EPOLLIN, {u32=4010170080, u64=94544830289632}}, {EPOLLIN, {u32=4010060672, u64=94544830180224}}], 11, 0) = 2

clock_gettime(CLOCK_REALTIME, {tv_sec=1524848329, tv_nsec=484799898}) = 0

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=112300760}) = 0

clock_gettime(CLOCK_BOOTTIME, {tv_sec=1045, tv_nsec=112454363}) = 0

epoll_wait(10, [{EPOLLIN, {u32=4010170080, u64=94544830289632}}, {EPOLLIN, {u32=4010060672, u64=94544830180224}}], 11, 0) = 2

clock_gettime(CLOCK_REALTIME, {tv_sec=1524848329, tv_nsec=485376240}) = 0

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=112893238}) = 0

clock_gettime(CLOCK_BOOTTIME, {tv_sec=1045, tv_nsec=113047679}) = 0

recvmsg(7, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="", iov_len=0}], msg_iovlen=1, msg_control=[{cmsg_len=28, cmsg_level=SOL_SOCKET, cmsg_type=SCM_CREDENTIALS, cmsg_data={pid=24957, uid=0, gid=0}}], msg_controllen=32, msg_flags=0}, MSG_DONTWAIT) = 0

recvmsg(7, {msg_namelen=0}, MSG_DONTWAIT) = -1 EAGAIN (Resource temporarily unavailable)

sendmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=-853365251, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base="libudev0376355312376(000(0003150005w3053452612Ge"..., iov_len=40}, {iov_base="ACTION=unbind0DEVPATH=/devices/p"..., iov_len=205}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, 0) = 245

epoll_wait(10, [{EPOLLIN, {u32=4010170080, u64=94544830289632}}], 11, 0) = 1

clock_gettime(CLOCK_REALTIME, {tv_sec=1524848329, tv_nsec=495431807}) = 0

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=123814890}) = 0

clock_gettime(CLOCK_BOOTTIME, {tv_sec=1045, tv_nsec=123945023}) = 0

recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=0x000001}, msg_namelen=128->12, msg_iov=[{iov_base="unbind@/devices/pci0000:00/0000:"..., iov_len=8192}], msg_iovlen=1, msg_control=[{cmsg_len=28, cmsg_level=SOL_SOCKET, cmsg_type=SCM_CREDENTIALS, cmsg_data={pid=0, uid=0, gid=0}}], msg_controllen=32, msg_flags=0}, 0) = 243

getrandom("x9cx6dx41x2bxb5xf0xf1x9ax32xb3x4ax73xeex04xffx90", 16, GRND_NONBLOCK) = 16

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=126971116}) = 0

getrandom("xafx35x7ax36x01x32xa6xe6x13x46x4ex22xccx48x77x9b", 16, GRND_NONBLOCK) = 16

getrandom("x48x0bxebxf1xf0x1cxf1x78x89xb7x48xe1x84x38xc9x3c", 16, GRND_NONBLOCK) = 16

getrandom("x11x06x8cx4axebxffx84x8ex0cx09x00x84x62x74xfcxd7", 16, GRND_NONBLOCK) = 16

getrandom("xb5x8ex19x16xadxf6x16x7ex21x66x90x12x2dx43x46x45", 16, GRND_NONBLOCK) = 16

getrandom("x84x7dx47x96x50x36xadx28x06x6exedx33xe0x05x57x20", 16, GRND_NONBLOCK) = 16

epoll_wait(10, [{EPOLLIN, {u32=4010170080, u64=94544830289632}}, {EPOLLIN, {u32=4010060672, u64=94544830180224}}], 11, 0) = 2

clock_gettime(CLOCK_REALTIME, {tv_sec=1524848329, tv_nsec=504542288}) = 0

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=131992368}) = 0

clock_gettime(CLOCK_BOOTTIME, {tv_sec=1045, tv_nsec=132096027}) = 0

epoll_wait(10, [{EPOLLIN, {u32=4010170080, u64=94544830289632}}, {EPOLLIN, {u32=4010060672, u64=94544830180224}}], 11, 0) = 2

clock_gettime(CLOCK_REALTIME, {tv_sec=1524848329, tv_nsec=504955877}) = 0

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=132438717}) = 0

clock_gettime(CLOCK_BOOTTIME, {tv_sec=1045, tv_nsec=132555928}) = 0

recvmsg(7, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="", iov_len=0}], msg_iovlen=1, msg_control=[{cmsg_len=28, cmsg_level=SOL_SOCKET, cmsg_type=SCM_CREDENTIALS, cmsg_data={pid=24957, uid=0, gid=0}}], msg_controllen=32, msg_flags=0}, MSG_DONTWAIT) = 0

recvmsg(7, {msg_namelen=0}, MSG_DONTWAIT) = -1 EAGAIN (Resource temporarily unavailable)

sendmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=-853365251, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base="libudev0376355312376(000(000231005w3053452612Ge"..., iov_len=40}, {iov_base="ACTION=bind0DEVPATH=/devices/pci"..., iov_len=275}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, 0) = 315

epoll_wait(10, [{EPOLLIN, {u32=4010170080, u64=94544830289632}}], 11, 0) = 1

clock_gettime(CLOCK_REALTIME, {tv_sec=1524848329, tv_nsec=512870505}) = 0

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=140367037}) = 0

clock_gettime(CLOCK_BOOTTIME, {tv_sec=1045, tv_nsec=140494166}) = 0

recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=0x000001}, msg_namelen=128->12, msg_iov=[{iov_base="bind@/devices/pci0000:00/0000:00"..., iov_len=8192}], msg_iovlen=1, msg_control=[{cmsg_len=28, cmsg_level=SOL_SOCKET, cmsg_type=SCM_CREDENTIALS, cmsg_data={pid=0, uid=0, gid=0}}], msg_controllen=32, msg_flags=0}, 0) = 311

getrandom("x21xcdx52xaex20xa4xe9x0fx2cx3fx68x8ax77x65xfbx22", 16, GRND_NONBLOCK) = 16

getrandom("xb5x1fx43xf7x14x3ex29x6cxddx95xd5x64xecxecx66xca", 16, GRND_NONBLOCK) = 16

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=141295429}) = 0

getrandom("xe7x73x2exc2x5dx71x93x8axd0xf4x5fxd7x91x1fx7bx00", 16, GRND_NONBLOCK) = 16

getrandom("xe4xd4xd3x2cxa2xa1x0cx96x6ex6ax34x9cx50x06x3dx43", 16, GRND_NONBLOCK) = 16

getrandom("xb0x7fxf7x93x1fxa6x6dx2ex01xfbx21x97x4bxe8x85x14", 16, GRND_NONBLOCK) = 16

getrandom("x3fx94x2bx17x01x8fx88x2ex08xa0x9dxd0xefx4fx0ex9a", 16, GRND_NONBLOCK) = 16

epoll_wait(10, [{EPOLLIN, {u32=4010170080, u64=94544830289632}}, {EPOLLIN, {u32=4010060672, u64=94544830180224}}], 11, 0) = 2

clock_gettime(CLOCK_REALTIME, {tv_sec=1524848329, tv_nsec=519062044}) = 0

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=146474265}) = 0

clock_gettime(CLOCK_BOOTTIME, {tv_sec=1045, tv_nsec=146513033}) = 0

epoll_wait(10, [{EPOLLIN, {u32=4010170080, u64=94544830289632}}, {EPOLLIN, {u32=4010060672, u64=94544830180224}}], 11, 0) = 2

clock_gettime(CLOCK_REALTIME, {tv_sec=1524848329, tv_nsec=519231922}) = 0

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=146636530}) = 0

clock_gettime(CLOCK_BOOTTIME, {tv_sec=1045, tv_nsec=146675297}) = 0

recvmsg(7, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="", iov_len=0}], msg_iovlen=1, msg_control=[{cmsg_len=28, cmsg_level=SOL_SOCKET, cmsg_type=SCM_CREDENTIALS, cmsg_data={pid=24957, uid=0, gid=0}}], msg_controllen=32, msg_flags=0}, MSG_DONTWAIT) = 0

recvmsg(7, {msg_namelen=0}, MSG_DONTWAIT) = -1 EAGAIN (Resource temporarily unavailable)

sendmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=-853365251, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base="libudev0376355312376(000(0003150005w3053452612Ge"..., iov_len=40}, {iov_base="ACTION=unbind0DEVPATH=/devices/p"..., iov_len=205}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, 0) = 245

epoll_wait(10, [{EPOLLIN, {u32=4010170080, u64=94544830289632}}], 11, 0) = 1

clock_gettime(CLOCK_REALTIME, {tv_sec=1524848329, tv_nsec=525080911}) = 0

clock_gettime(CLOCK_MONOTONIC, {tv_sec=1045, tv_nsec=152528058}) = 0

clock_gettime(CLOCK_BOOTTIME, {tv_sec=1045, tv_nsec=152611810}) = 0

....

running udevadm monitor prints the following repeatedly:

KERNEL[1464.842652] bind     /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0 (usb)

KERNEL[1464.844393] unbind   /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0 (usb)

UDEV  [1464.845340] bind     /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0 (usb)

KERNEL[1464.857728] bind     /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0 (usb)

KERNEL[1464.858361] unbind   /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0 (usb)

....

and running journalctl returns repeatedly:

Apr 27 05:22:09 amir-pc systemd-udevd[359]: Process 'hid2hci --method=dell --devpath=/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3

Apr 27 05:22:09 amir-pc upowerd[1339]: unhandled action 'unbind' on /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0

-- Logs begin at Fri 2018-04-27 05:22:09 +0430, end at Fri 2018-04-27 21:37:15 +0430. --

Apr 27 05:22:09 amir-pc systemd-udevd[359]: Process 'hid2hci --method=dell --devpath=/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3

Apr 27 05:22:09 amir-pc upowerd[1339]: unhandled action 'unbind' on /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0

Apr 27 05:22:09 amir-pc systemd-udevd[359]: Process 'hid2hci --method=dell --devpath=/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3

Apr 27 05:22:09 amir-pc upowerd[1339]: unhandled action 'bind' on /sys/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0

....

running dmesg returns:

[  441.582359] usb 3-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0

[  441.582361] usb 3-1.3: Product: Dell Wireless 370 Bluetooth Mini-card

[  441.582363] usb 3-1.3: Manufacturer: Dell Computer Corp

[  450.803644] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.811642] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.819653] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.826650] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.833668] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.841644] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.848630] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.856628] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.863632] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.871611] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.881629] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.888616] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.896634] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.903596] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.910611] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.917595] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.926603] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.933598] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.942616] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.949606] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.957363] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.964607] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.973581] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.980582] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.987582] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  450.994561] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  451.004574] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  451.009525] ERROR @wl_cfg80211_scan : 

[  451.009527] WLC_SCAN error (-22)

[  451.010550] usb 3-1.2: usbfs: USBDEVFS_CONTROL failed cmd hid2hci rqt 33 rq 9 len 4 ret -71

[  451.020078] usb 3-1: USB disconnect, device number 14

[  451.020081] usb 3-1.1: USB disconnect, device number 15

[  451.076974] usb 3-1.2: USB disconnect, device number 16

[  451.077105] usb 3-1.3: USB disconnect, device number 19

[  796.468102] usb 3-1: new full-speed USB device number 20 using uhci_hcd

[  796.672318] usb 3-1: New USB device found, idVendor=0a5c, idProduct=4500

[  796.672322] usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0

[  796.672325] usb 3-1: Product: BCM2046B1

[  796.672328] usb 3-1: Manufacturer: Broadcom

[  796.674239] hub 3-1:1.0: USB hub found

[  796.676385] hub 3-1:1.0: 3 ports detected

[  796.976059] usb 3-1.1: new full-speed USB device number 21 using uhci_hcd

[  797.109323] usb 3-1.1: New USB device found, idVendor=413c, idProduct=8157

[  797.109332] usb 3-1.1: New USB device strings: Mfr=0, Product=0, SerialNumber=0

[  797.116785] input: HID 413c:8157 as /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.1/3-1.1:1.0/0003:413C:8157.000B/input/input25

[  797.176461] hid-generic 0003:413C:8157.000B: input,hidraw0: USB HID v1.11 Keyboard [HID 413c:8157] on usb-0000:00:1a.0-1.1/input0

[  797.256314] usb 3-1.2: new full-speed USB device number 22 using uhci_hcd

[  797.396307] usb 3-1.2: New USB device found, idVendor=413c, idProduct=8158

[  797.396315] usb 3-1.2: New USB device strings: Mfr=0, Product=0, SerialNumber=0

[  797.405072] input: HID 413c:8158 as /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0/0003:413C:8158.000C/input/input26

[  797.464858] hid-generic 0003:413C:8158.000C: input,hidraw3: USB HID v1.11 Mouse [HID 413c:8158] on usb-0000:00:1a.0-1.2/input0

[  797.564507] IPv6: ADDRCONF(NETDEV_UP): wlp4s0: link is not ready

[  797.944045] usb 3-1.3: new full-speed USB device number 23 using uhci_hcd

[  803.296508] usb 3-1.3: unable to read config index 0 descriptor/all

[  803.296515] usb 3-1.3: can't read configurations, error -110

[  803.376039] usb 3-1.3: new full-speed USB device number 24 using uhci_hcd

[  808.672986] usb 3-1.3: unable to read config index 0 descriptor/all

[  808.672993] usb 3-1.3: can't read configurations, error -110

[  808.673984] usb 3-1-port3: attempt power cycle

[  809.280029] usb 3-1.3: new full-speed USB device number 25 using uhci_hcd

[  809.340944] usb 3-1.3: New USB device found, idVendor=413c, idProduct=8156

[  809.340948] usb 3-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0

[  809.340951] usb 3-1.3: Product: Dell Wireless 370 Bluetooth Mini-card

[  809.340954] usb 3-1.3: Manufacturer: Dell Computer Corp

[ 1337.985097] perf: interrupt took too long (2508 > 2500), lowering kernel.perf_event_max_sample_rate to 79500

[ 1387.269440] perf: interrupt took too long (3140 > 3135), lowering kernel.perf_event_max_sample_rate to 63500

[ 1454.553305] perf: interrupt took too long (3927 > 3925), lowering kernel.perf_event_max_sample_rate to 50750

....

and running /lib/systemd/systemd-udevd -D returns below results repeatedly:

IMPORT builtin 'hwdb' /lib/udev/rules.d/50-udev-default.rules:14

RUN 'hid2hci --method=dell --devpath=%p' /lib/udev/rules.d/97-hid2hci.rules:11

starting 'hid2hci --method=dell --devpath=/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0'

seq 284188 queued, 'bind' 'usb'

seq 284189 queued, 'unbind' 'usb'

'hid2hci --method=dell --devpath=/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0'(err) 'error: switching device '/sys//devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0' failed.'

Process 'hid2hci --method=dell --devpath=/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0' failed with exit code 1.

seq 284184 processed

seq 284185 running

RUN 'hid2hci --method=dell --devpath=%p' /lib/udev/rules.d/97-hid2hci.rules:11

starting 'hid2hci --method=dell --devpath=/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.2/3-1.2:1.0'

seq 284190 queued, 'bind' 'usb'

seq 284191 queued, 'unbind' 'usb'

My fresh installed Kubuntu is using kernel version 4.15.0-20-generic and my laptop is a Dell Studio XPS 1640. WiFi is using bcmwl-kernel-source 6.30.223.271+bdcom-0ubuntu4 driver (downgrading to a previous working driver didn't solve the problem).

It's worth mentioning that no USB devices are connected, only a wireless mouse, which makes no problem (disconnecting it doesn't affect the problem). But as mentioned turning off WiFi always make the high CPU load disappear.