I wanted to check a CD from my drawer. I inserted it into my drive and issued mount. I got
mount: block device /dev/sr0 is write-protected, mounting read-only
mount command did not exit. I checked its state in top:
4640 root 20 0 27088 1280 1060 R 99,8 0,0 1:36.90 mount
99,8% CPU usage what was not true because usage of all my cores is almost 0,0%. I tried to kill it - no success (both signals KILL and TERM fail to stop the mount programme). I tried reboot -f and reboot got into D state. fuser helped neither. /dev/sr0 is my cdrom and it was not present in mount output
umount /media/cdrom umount: /media/cdrom0 is not mounted (according to mtab)
/dev/sr0 /media/cdrom0 udf,iso9660 user,noauto 0 0
Don't know what to do with that. All what works is to cut power and start again. System doesn't reboot or shutdown.