Thanks. Especially that second link seems very much more plausible in its analysis “This is probably a simple check assertion somewhere which is seeing unexpected data passing through a call”
If you write a file system every bug can destroy years of data, silently, so “better be safe then sorry” should be a poster hanging on every wall, so even a simple directory traversal, upon seeing a “this normally shouldn’t happen” event, should raise a few flags.
It appears that the file system is not actually corrupted. The bug is just triggering a warning popup and a consistency check at the next boot. [1]
[0] https://news.ycombinator.com/item?id=25787717 [1] https://news.ycombinator.com/item?id=25788171