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    SubjectRe: ext3fs: umount+sync not enough to guarantee metadata-on-disk
    Andrew Morton wrote:
    > On Thu, 07 Jun 2007 12:11:58 -0400
    > Chuck Ebbert <> wrote:
    >> On 06/07/2007 11:41 AM, Andrew Morton wrote:
    >>>> mount /var/lib/mythtv -oremount,ro
    >>>> sync
    >>>> umount /var/lib/mythtv
    >>> Did this succeed? If the application is still truncating that file, the
    >>> umount should have failed.
    >> Shouldn't sync should wait for truncate to finish?
    > I can't think of anything in there at present which would cause that to
    > happen, and it's not immediately obvious how we _could_ make it happen - we
    > have an inode which potentially has no dirty pages and which is itself
    > clean. The truncate can span multiple journal commits, so forcing a
    > journal commit in sync() won't necessarily block behind the truncate.
    > I guess we could ask sync to speculatively take and release every inode's
    > i_mutex or something. But even that would involve quite some hoop-jumping
    > due to those infuriating spinlock-protected list_heads on the superblock.
    > hmm.

    Okay, I added more instrumentation and retested today.

    Good and Bad.
    The umount does indeed fail while the massive unlink is happening,
    so I can just loop on that a few times before giving up.

    But.. the earlier "remount,ro".. well.. I don't know what it does.
    I did get it to lock up solid, though.. hung on the "remount,ro"
    when issued during an unlink of a 15GB file. The disk I/O eventually
    completes, and drives go idle, but the system remains hung inside
    the remount,ro call.

    Alt-sysrq-T was functioning, so I have some screen shots (.jpg) here:

    That's definitely a bug.
    For now, I'll just not attempt the remount,ro on this system,
    and have it loop for a minute attempting umount instead.

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