Chris Mason wrote:

write log blocks
flush #1
write commit block
flush #2
write metadata blocks

I'd agree with Ted, there's a fairly small chance of things get reordered 
around flush #1.

Except when it crosses an MD disk boundary.  Then it's really likely.

We could also ask if there's _any_ possibility, when they are a merged
single I/O, of them not getting written in the expected order?
What about when FUA is set, does that imply any order?

But it's all moot: Checksumming is the way forward here, no doubt.
Checksumming makes the multi-sector write "atomic or corrupt".  That's
the same expectation as a commit sector provides by itself, but
generalised to the whole journal entry.

-- Jamie