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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:
    Thanks for the traces.

    > That's definitely a bug.
    Yes. We have a nice lock inversion there. ext3_remount() is called
    with sb->s_lock held and waits for transaction to finish in
    journal_lock_updates(). On the other hand ext3_orphan_del() is called
    inside a transaction and tries to do lock_super()... Bad luck.


    Jan Kara <>
    SuSE CR Labs
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