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    SubjectRe: 2.6.22-rc3 hibernate(?) fails totally - regression (xfs on raid6)
    On Thu, Jun 07, 2007 at 02:59:58PM +0100, David Greaves wrote:
    > David Chinner wrote:
    > >On Thu, Jun 07, 2007 at 11:30:05AM +0100, David Greaves wrote:
    > >>Tejun Heo wrote:
    > >>>Hello,
    > >>>
    > >>>David Greaves wrote:
    > >>>>Just to be clear. This problem is where my system won't resume after s2d
    > >>>>unless I umount my xfs over raid6 filesystem.
    > >>>This is really weird. I don't see how xfs mount can affect this at all.
    > >>Indeed.
    > >>It does :)
    > >
    > >Ok, so lets determine if it really is XFS.
    > Seems like a good next step...
    > >Does the lockup happen with a
    > >different filesystem on the md device? Or if you can't test that, does
    > >any other XFS filesystem you have show the same problem?
    > It's a rather full 1.2Tb raid6 array - can't reformat it - sorry :)

    I suspected as much :/

    > I only noticed the problem when I umounted the fs during tests to prevent
    > corruption - and it worked. I'm doing a sync each time it hibernates (see
    > below) and a couple of paranoia xfs_repairs haven't shown any problems.

    sync just guarantees that metadata changes are logged and data is
    on disk - it doesn't stop the filesystem from doing anything after
    the sync...

    > I do have another xfs filesystem on /dev/hdb2 (mentioned when I noticed the
    > md/XFS correlation). It doesn't seem to have/cause any problems.

    Ok, so it's not an obvious XFS problem...

    > >If it is xfs that is causing the problem, what happens if you
    > >remount read-only instead of unmounting before shutting down?
    > Yes, I'm happy to try these tests.
    > nb, the hibernate script is:
    > ethtool -s eth0 wol g
    > sync
    > echo platform > /sys/power/disk
    > echo disk > /sys/power/state
    > So there has always been a sync before any hibernate.
    > cu:~# mount -oremount,ro /huge
    > [this works and resumes]


    > cu:~# mount -oremount,rw /huge
    > cu:~# /usr/net/bin/hibernate
    > [this works and resumes too !]

    Interesting. That means something in the generic remount code
    is affecting this.

    > cu:~# touch /huge/tst
    > cu:~# /usr/net/bin/hibernate
    > [but this doesn't even hibernate]

    Ok, so a clean inode is sufficient to prevent hibernate from working.

    So, what's different between a sync and a remount?

    do_remount_sb() does:

    599 shrink_dcache_sb(sb);
    600 fsync_super(sb);

    of which a sync does neither. sync does what fsync_super() does in
    different sort of way, but does not call sync_blockdev() on each
    block device. It looks like that is the two main differences between
    sync and remount - remount trims the dentry cache and syncs the blockdev,
    sync doesn't.

    > > What about freezing the filesystem?
    > cu:~# xfs_freeze -f /huge
    > cu:~# /usr/net/bin/hibernate
    > [but this doesn't even hibernate - same as the 'touch']

    I suspect that the frozen filesystem might cause other problems
    in the hibernate process. However, while a freeze calls sync_blockdev()
    it does not trim the dentry cache.....

    So, rather than a remount before hibernate, lets see if we can
    remove the dentries some other way to determine if removing excess
    dentries/inodes from the caches makes a difference. Can you do:

    # touch /huge/foo
    # sync
    # echo 1 > /proc/sys/vm/drop_caches
    # hibernate

    # touch /huge/bar
    # sync
    # echo 2 > /proc/sys/vm/drop_caches
    # hibernate

    # touch /huge/baz
    # sync
    # echo 3 > /proc/sys/vm/drop_caches
    # hibernate

    And see if any of those survive the suspend/resume?


    Dave Chinner
    Principal Engineer
    SGI Australian Software Group
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      Last update: 2007-06-08 00:31    [W:0.027 / U:8.116 seconds]
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