Recent Linux kernels (4.0.2+, LTS 3.14.41+), pushed to the [core] repository in the past couple of weeks, suffered from a bug that can cause data corruption on file systems mounted with the discard option and residing on software RAID 0 arrays. Even if discard is not specified, the fstrim command can also trigger this bug. (If you do not use software RAID 0 or the discard option, then this issue does not affect you.)
The issue has been addressed in the linux 4.0.4-2 and linux-lts 3.14.43-2 updates. Due to the nature of the bug, however, it is likely that data corruption has already occurred on systems running the aforementioned kernels. It is strongly advised to verify the integrity of affected file systems using fsck and/or restore their data from known good backups.
For further information please read the LKML post by Holger Kiehl, the related article on Phoronix, as well as the proposed fix that was backported to the Arch kernels.