Weirdly, my system froze again.

The good news is that, this time is not caused by hard drive. However, the bad news is I don't know who caused it.

The dmesg said there is nothing wrong with the system and I can check the message after reboot. The only clue is that I switched from the browser back to IDEA, and everything froze and the gnome stops responding. Mouse doesn't move, no response from keyboard, and I tried REISUB and looks like some of the sysrq are disabled.