Meanwhile I was able to identify more by removing "quiet" from the grub loader.
The pcc_cpufreq_init does not seem to hurt the booting - these are just warnings popping up.
The following messages appear on the console before the server freezes:
[ OK ] Finished Load Kernel Module fuse.
[ 62.887855] systemd[1]: Mounting FUSE Control File System...
Mounting FUSE Controle File System...
[ 62.891852] systemd[1]: Finished Apply Kernel Variables.
[ OK ] Finished Apply Kernel Variables.
[ 62.892237] systemd[1]: Mounted FUSE Control File System.
[ OK ] Mounted FUSE Control File System.
[ 62.900668] systemd[1]: Finished Create System Users.
[ OK ] Finished Create System Users.
[ 62.902224] systemd[1]: Starting Create Static Device Nodes in /dev...
Starting Create Static Device Nodes in /dev...
[ 62.920767] systemd[1]: modprobe@drm.service: Succeeded.
[ 62.921202] systemd[1]: Finished Load Kernel Module drm.
[ OK ] Finished Load Kernel Module drm.
[ 62.921979] systemd[1]: Finished Create Static Device Nodes in /dev.
[ OK ] Finished Create Static Device Nodes in /dev.
[ 62.925007] systemd[1]: Starting Rule-based Manager for Device Events and Files...
Starting Rule-based Manager for Device Events and Files...
[ 62.955322] systemd[1]: Finished Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress polling.
[ OK ] Finished Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress polling.
[ 62.962186] systemd[1]: Started Rule-based Manager for Device Events and Files.
After this, no further messages, no login prompt, server does not react to keyboard input anymore. Only a hardware reset works in this case.
Out of ~10 server reboots this problem occurred 4 or 5 times.
Could it have something to do with drm? I've seen a drm driver error during earlier boot phase.
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.182074] [drm] radeon kernel modesetting enabled.
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.182197] radeon 0000:01:03.0: vgaarb: deactivate vga console
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.183720] Console: switching to colour dummy device 80x25
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184088] [drm] initializing kernel modesetting (RV100 0x1002:0x515E 0x103C:0x31FB 0x02).
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184208] radeon 0000:01:03.0: VRAM: 128M 0x00000000E8000000 - 0x00000000EFFFFFFF (64M used)
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184210] radeon 0000:01:03.0: GTT: 512M 0x00000000C8000000 - 0x00000000E7FFFFFF
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184219] [drm] Detected VRAM RAM=128M, BAR=128M
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184220] [drm] RAM width 16bits DDR
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184302] [TTM] Zone kernel: Available graphics memory: 49487844 KiB
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184304] [TTM] Zone dma32: Available graphics memory: 2097152 KiB
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184305] [TTM] Initializing pool allocator
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184310] [TTM] Initializing DMA pool allocator
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184333] [drm] radeon: 64M of VRAM memory ready
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184334] [drm] radeon: 512M of GTT memory ready.
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.184371] [drm] GART: num cpu pages 131072, num gpu pages 131072
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.205645] [drm] PCI GART of 512M enabled (table at 0x00000000FFF00000).
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.205890] radeon 0000:01:03.0: WB disabled
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.205894] radeon 0000:01:03.0: fence driver on ring 0 use gpu addr 0x00000000c8000000
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.205967] [drm] radeon: irq initialized.
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.205980] [drm] Loading R100 Microcode
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206233] radeon 0000:01:03.0: firmware: failed to load radeon/R100_cp.bin (-2)
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206241] firmware_class: See
https://wiki.debian.org/Firmware for information about missing firmware
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206246] radeon 0000:01:03.0: Direct firmware load for radeon/R100_cp.bin failed with error -2
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206311] [drm:r100_cp_init [radeon]] *ERROR* Failed to load firmware!
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206318] radeon 0000:01:03.0: failed initializing CP (-2).
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206321] radeon 0000:01:03.0: Disabling GPU acceleration
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206329] [drm] radeon: cp finalized
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206961] [drm] No TV DAC info found in BIOS
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206996] [drm] Radeon Display Connectors
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206997] [drm] Connector 0:
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206998] [drm] VGA-1
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.206999] [drm] DDC: 0x60 0x60 0x60 0x60 0x60 0x60 0x60 0x60
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.207000] [drm] Encoders:
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.207001] [drm] CRT1: INTERNAL_DAC1
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.207002] [drm] Connector 1:
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.207003] [drm] VGA-2
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.207004] [drm] DDC: 0x6c 0x6c 0x6c 0x6c 0x6c 0x6c 0x6c 0x6c
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.207004] [drm] Encoders:
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.207005] [drm] CRT2: INTERNAL_DAC2
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.236242] kvm: VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL does not work properly. Using workaround
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.245005] EXT4-fs (dm-0): mounted filesystem with ordered data mode. Opts: (null)
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.250269] [drm] fb mappable at 0xE8040000
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.250270] [drm] vram apper at 0xE8000000
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.250271] [drm] size 1572864
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.250271] [drm] fb depth is 16
Jun 28 16:15:05 irczsrvp08 kernel: [ 63.250272] [drm] pitch is 2048