Merge branch 'for-linus' of git://neil.brown.name/md

* 'for-linus' of git://neil.brown.name/md:
md: allow upper limit for resync/reshape to be set when array is read-only
md/raid5: Properly remove excess drives after shrinking a raid5/6
md/raid5: make sure a reshape restarts at the correct address.
md/raid5: allow new reshape modes to be restarted in the middle.
md: never advance 'events' counter by more than 1.
Remove deadlock potential in md_open

drivers/md/md.c

···
 	else
 		new->md_minor = MINOR(unit) >> MdpMinorShift;
 
+	mutex_init(&new->open_mutex);
 	mutex_init(&new->reconfig_mutex);
 	INIT_LIST_HEAD(&new->disks);
 	INIT_LIST_HEAD(&new->all_mddevs);
···
 		/* otherwise we have to go forward and ... */
 		mddev->events ++;
 		if (!mddev->in_sync || mddev->recovery_cp != MaxSector) { /* not clean */
-			/* .. if the array isn't clean, insist on an odd 'events' */
-			if ((mddev->events&1)==0) {
-				mddev->events++;
+			/* .. if the array isn't clean, an 'even' event must also go
+			 * to spares. */
+			if ((mddev->events&1)==0)
 				nospares = 0;
-			}
 		} else {
-			/* otherwise insist on an even 'events' (for clean states) */
-			if ((mddev->events&1)) {
-				mddev->events++;
+			/* otherwise an 'odd' event must go to spares */
+			if ((mddev->events&1))
 				nospares = 0;
-			}
 		}
 	}
 
···
 		if (max < mddev->resync_min)
 			return -EINVAL;
 		if (max < mddev->resync_max &&
+		    mddev->ro == 0 &&
 		    test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
 			return -EBUSY;
 
···
 	struct gendisk *disk = mddev->gendisk;
 	mdk_rdev_t *rdev;
 
+	mutex_lock(&mddev->open_mutex);
 	if (atomic_read(&mddev->openers) > is_open) {
 		printk("md: %s still in use.\n",mdname(mddev));
-		return -EBUSY;
-	}
-
-	if (mddev->pers) {
+		err = -EBUSY;
+	} else if (mddev->pers) {
 
 		if (mddev->sync_thread) {
 			set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
···
 			set_disk_ro(disk, 1);
 		clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
 	}
-
+out:
+	mutex_unlock(&mddev->open_mutex);
+	if (err)
+		return err;
 	/*
 	 * Free resources if final stop
 	 */
···
 	blk_integrity_unregister(disk);
 	md_new_event(mddev);
 	sysfs_notify_dirent(mddev->sysfs_state);
-out:
 	return err;
 }
 
···
 	}
 	BUG_ON(mddev != bdev->bd_disk->private_data);
 
-	if ((err = mutex_lock_interruptible_nested(&mddev->reconfig_mutex, 1)))
+	if ((err = mutex_lock_interruptible(&mddev->open_mutex)))
 		goto out;
 
 	err = 0;
 	atomic_inc(&mddev->openers);
-	mddev_unlock(mddev);
+	mutex_unlock(&mddev->open_mutex);
 
 	check_disk_change(bdev);
  out:

drivers/md/md.h

···
 							    * so we don't loop trying */
 
 	int				in_sync;	/* know to not need resync */
+	/* 'open_mutex' avoids races between 'md_open' and 'do_md_stop', so
+	 * that we are never stopping an array while it is open.
+	 * 'reconfig_mutex' protects all other reconfiguration.
+	 * These locks are separate due to conflicting interactions
+	 * with bdev->bd_mutex.
+	 * Lock ordering is:
+	 *  reconfig_mutex -> bd_mutex : e.g. do_md_run -> revalidate_disk
+	 *  bd_mutex -> open_mutex:  e.g. __blkdev_get -> md_open
+	 */
+	struct mutex			open_mutex;
 	struct mutex			reconfig_mutex;
 	atomic_t			active;		/* general refcount */
 	atomic_t			openers;	/* number of active opens */

drivers/md/raid5.c

···
 		    conf->reshape_progress < raid5_size(mddev, 0, 0)) {
 			sector_nr = raid5_size(mddev, 0, 0)
 				- conf->reshape_progress;
-		} else if (mddev->delta_disks > 0 &&
+		} else if (mddev->delta_disks >= 0 &&
 			   conf->reshape_progress > 0)
 			sector_nr = conf->reshape_progress;
 		sector_div(sector_nr, new_data_disks);
···
 			   (old_disks-max_degraded));
 		/* here_old is the first stripe that we might need to read
 		 * from */
-		if (here_new >= here_old) {
+		if (mddev->delta_disks == 0) {
+			/* We cannot be sure it is safe to start an in-place
+			 * reshape.  It is only safe if user-space if monitoring
+			 * and taking constant backups.
+			 * mdadm always starts a situation like this in
+			 * readonly mode so it can take control before
+			 * allowing any writes.  So just check for that.
+			 */
+			if ((here_new * mddev->new_chunk_sectors != 
+			     here_old * mddev->chunk_sectors) ||
+			    mddev->ro == 0) {
+				printk(KERN_ERR "raid5: in-place reshape must be started"
+				       " in read-only mode - aborting\n");
+				return -EINVAL;
+			}
+		} else if (mddev->delta_disks < 0
+		    ? (here_new * mddev->new_chunk_sectors <=
+		       here_old * mddev->chunk_sectors)
+		    : (here_new * mddev->new_chunk_sectors >=
+		       here_old * mddev->chunk_sectors)) {
 			/* Reading from the same stripe as writing to - bad */
 			printk(KERN_ERR "raid5: reshape_position too early for "
 			       "auto-recovery - aborting.\n");
···
 					mddev->degraded--;
 			for (d = conf->raid_disks ;
 			     d < conf->raid_disks - mddev->delta_disks;
-			     d++)
-				raid5_remove_disk(mddev, d);
+			     d++) {
+				mdk_rdev_t *rdev = conf->disks[d].rdev;
+				if (rdev && raid5_remove_disk(mddev, d) == 0) {
+					char nm[20];
+					sprintf(nm, "rd%d", rdev->raid_disk);
+					sysfs_remove_link(&mddev->kobj, nm);
+					rdev->raid_disk = -1;
+				}
+			}
 		}
 		mddev->layout = conf->algorithm;
 		mddev->chunk_sectors = conf->chunk_sectors;