BUG: aio/direct-io data corruption in 4.7

[Jonathan Nicklin]

In 4.7.2, the kernel is acknowledging block writes that have not
completed to disk. To reproduce: create an MD array, run FIO (direct +
libaio), and pull all drives. FIO will continue to run without
receiving I/O errors. I have also reproduced the bug using physical
drives. In this case, only a limited number of I/Os are incorrectly
acknowledged; FIO eventually receives an I/O error after the device
reference is removed.

The root cause of the problem is that dio_complete() does not
correctly propagate I/O errors in the is_async case. Specifically,
generic_write_sync() appears to be overwriting the return status
destined for ki_complete().

This bug appears to have been introduced by the following commit:

Description: "fs: simplify the generic_write_sync prototype"
Committed: Apr 7, 2016
Hash: e259221763a40403d5bb232209998e8c45804ab8
Affects: 4.7-rc1 - master

I have confirmed a fix for the AIO/Direct-IO failure condition but
have not reviewed the rest of the changes associated with that commit.
If you would like a small patch for direct-io.c, let me know.

Regards,
-Jonathan