For other people who didn't immediately recognize "ITS and the PC2 problem" and want the backstory it starts in the last paragraph of page 312: https://web.mit.edu/~simsong/www/ugh.pdf

I have a reproducible way to have a pwrite syscall on a specific SSD on a specific machine take 15+ seconds and completely block any syscall related to that SSD by any other thread or core during that amount of time. I tried and couldn't preempt it either (sched_fifo and preempt kernel options). I should have a look soon with Intel PT to check whether it's on the same instruction every time :)

Oh, it totally is, it just doesn't prompt the same sense of glee and wonderment.