So... one can, on a filesystem that is mirrored using MD RAID, from userspace, and with no special permissions (as it seems O_DIRECT does not require any), create a standard-looking file that has two different possible contents, depending from which RAID mirror it happens to be read from today? And, this bug, which has been open for a decade now, has, somehow, not been considered to be an all-hands-on-deck security issue that undermines the integrity of every single mechanism people might ever use to validate the content of a file, because... checks notes... we should instead be "teaching [the attacker] not to use [O_DIRECT]"?

(FWIW, I appreciate the performance impact of a full fix here might be brutal, but the suggestion of requiring boot-args opt-in for O_DIRECT in these cases should not have been ignored, as there are a ton of people who might not actively need or even be using O_DIRECT, and the people who do should be required to know what they are getting into.)