Pointer compare in md driver

Hi,

I have a question when reading md driver. Following is the code from
linux/drivers/md/md.c, function md_do_sync():

>                 for_each_mddev(mddev2, tmp) {
>                         if (mddev2 == mddev)
>                                 continue;
>                         if (!mddev->parallel_resync
>                         &&  mddev2->curr_resync
>                         &&  match_mddev_units(mddev, mddev2)) {
>                                 DEFINE_WAIT(wq);
>                                 if (mddev < mddev2 && mddev->curr_resync == 2) {
>                                         /* arbitrarily yield */
>                                         mddev->curr_resync = 1;
>                                         wake_up(&resync_wait);
>                                 }
>                                 if (mddev > mddev2 && mddev->curr_resync == 1)
>                                         /* no need to wait here, we can wait the next
>                                          * time 'round when curr_resync == 2
>                                          */
>                                         continue;
>                                 /* We need to wait 'interruptible' so as not to

The type of mddev2 and mddev both are struct mddev *, so what's the
meaning of comparing these two variables?

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