On 10/24/2012 12:23 AM, Theodore Ts'o wrote:

On Tue, Oct 23, 2012 at 11:27:09PM -0500, Eric Sandeen wrote:

quoted

Ok, fair enough.  If the BBU is working, nobarrier is ok; I don't trust
journal_async_commit, but that doesn't mean this isn't a regression.

Note that Toralf has reported almost exactly the same set of symptoms,
but he's using an external USB stick --- and as far as I know he
wasn't using nobarrier and/or the journal_async_commit.  Toralf, can
you confirm what, if any, mount options you were using when you saw
it.

I've been looking at this some more, and there's one other thing that
the short circuit code does, which is neglects setting the
JBD2_FLUSHED flag, which is used by the commit code to know when it
needs to reset the s_start fields in the superblock when we make our
next commit.  However, this would only happen if the short circuit
code is getting hit some time other than when the file system is
getting unmounted --- and that's what Eric and I can't figure out how
it might be happening.  Journal flushes outside of an unmount does
happen as part of online resizing, the FIBMAP ioctl, or when the file
system is frozen.  But it didn't sound like Toralf or Nix was using
any of those features.  (Toralf, Nix, please correct me if my
assumptions here is wrong).

If I freeze w/ anything in the log, then s_start !=0 and we proceed
normally.  If I re-freeze w/o anything in the log, it's already set to
FLUSHED (which makes sense) so not re-setting it doesn't matter.  So I
don't see that that's an issue.

As for FIBMAP I think we only do journal_flush if it's data=journal.

In other news, Phoronix is on the case, so expect escalating freakouts ;)

-Eric