• Benjamin Marzinski's avatar
    GFS2: update freeze code to use freeze/thaw_super on all nodes · 2e60d768
    Benjamin Marzinski authored
    The current gfs2 freezing code is considerably more complicated than it
    should be because it doesn't use the vfs freezing code on any node except
    the one that begins the freeze.  This is because it needs to acquire a
    cluster glock before calling the vfs code to prevent a deadlock, and
    without the new freeze_super and thaw_super hooks, that was impossible. To
    deal with the issue, gfs2 had to do some hacky locking tricks to make sure
    that a frozen node couldn't be holding on a lock it needed to do the
    unfreeze ioctl.
    
    This patch makes use of the new hooks to simply the gfs2 locking code. Now,
    all the nodes in the cluster freeze and thaw in exactly the same way. Every
    node in the cluster caches the freeze glock in the shared state.  The new
    freeze_super hook allows the freezing node to grab this freeze glock in
    the exclusive state without first calling the vfs freeze_super function.
    All the nodes in the cluster see this lock change, and call the vfs
    freeze_super function. The vfs locking code guarantees that the nodes can't
    get stuck holding the glocks necessary to unfreeze the system.  To
    unfreeze, the freezing node uses the new thaw_super hook to drop the freeze
    glock. Again, all the nodes notice this, reacquire the glock in shared mode
    and call the vfs thaw_super function.
    Signed-off-by: default avatarBenjamin Marzinski <bmarzins@redhat.com>
    Signed-off-by: Steven Whitehouse's avatarSteven Whitehouse <swhiteho@redhat.com>
    2e60d768
super.h 1.93 KB