Some tl;dr takeaways :

I was shocked that nobody had ever noticed this bug in the mainline kernel, but that’s what happened. I guess to be more accurate, the OLPC project did notice it at one point, but since they had a workaround it wasn’t a huge deal. I decided to go ahead and fix the underlying problem.

I first submitted my fix for this problem in September 2022, but I didn’t receive any responses. I ended up resubmitting it later that year and CCing the main SoC maintainers the second time, and they took care of merging my fix. It was finally released with Linux 6.2 and was also backported to several 4.x, 5.x, and 6.x kernels. Ever since I implemented this fix, I haven’t noticed any problems with CPU time reporting on my Chumby.

It was very satisfying to be able to fix the problem! The time I spent was totally worth it too. I learned all about how procfs works and how top gets its info about CPU usage. I still feel like I know almost nothing about the internals of the Linux kernel, but solving a problem like this was a fantastic way to dip my toes into it.