Comment by jeltz
It is possible to corrupt the file system from user space as a normal user with Btrfs. The PostgreSQL devs found that when working on async IO. And as fer as I know that issue has not been fixed.
https://www.postgresql.org/message-id/CA%2BhUKGL-sZrfwcdme8j...
LMDB users also unearthed a btrfs data corruption bug last year: https://bugzilla.redhat.com/show_bug.cgi?id=2169947