EC concurrent PUT same file success but file is corrupt

[bakawang]

If two request PUT the same file name at same time, it's possible that one of requests success but file is corrupt.

This is what happens:

1. Swift use EC and encryption at rest.
2. Request A and Request B PUT same file at same time (A's content will different from B's because of encryption).
2. Object server process A and process B PUT same name file with same timestamp(1234567890.12345).
3. Process A writes finish and linkat 1234567890.12345#1.data success.
4. Process B writes finish and try to linkat 1234567890.12345#1.data.
5. Process B linkat fail and unlink original 1234567890.12345#1.data then re-linkat success.
6. Process A receives commit command and rename 1234567890.123455#1.data(generated by B) to 1234567890.12345#1#d.data
7. Request A returns success and request B fail, but if A's fragments generated by B more than parity the file becomes corrupt.

Environment:
swift version - wallaby