diff --git a/block/genhd.c b/block/genhd.c
index ee4b13520e5..67e5a59ced2 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -298,6 +298,38 @@ EXPORT_SYMBOL(unregister_blkdev);
 
 static struct kobj_map *bdev_map;
 
+/**
+ * blk_mangle_minor - scatter minor numbers apart
+ * @minor: minor number to mangle
+ *
+ * Scatter consecutively allocated @minor number apart if MANGLE_DEVT
+ * is enabled.  Mangling twice gives the original value.
+ *
+ * RETURNS:
+ * Mangled value.
+ *
+ * CONTEXT:
+ * Don't care.
+ */
+static int blk_mangle_minor(int minor)
+{
+#ifdef CONFIG_DEBUG_BLOCK_EXT_DEVT
+	int i;
+
+	for (i = 0; i < MINORBITS / 2; i++) {
+		int low = minor & (1 << i);
+		int high = minor & (1 << (MINORBITS - 1 - i));
+		int distance = MINORBITS - 1 - 2 * i;
+
+		minor ^= low | high;	/* clear both bits */
+		low <<= distance;	/* swap the positions */
+		high >>= distance;
+		minor |= low | high;	/* and set */
+	}
+#endif
+	return minor;
+}
+
 /**
  * blk_alloc_devt - allocate a dev_t for a partition
  * @part: partition to allocate dev_t for
@@ -339,7 +371,7 @@ int blk_alloc_devt(struct hd_struct *part, dev_t *devt)
 		return -EBUSY;
 	}
 
-	*devt = MKDEV(BLOCK_EXT_MAJOR, idx);
+	*devt = MKDEV(BLOCK_EXT_MAJOR, blk_mangle_minor(idx));
 	return 0;
 }
 
@@ -361,7 +393,7 @@ void blk_free_devt(dev_t devt)
 
 	if (MAJOR(devt) == BLOCK_EXT_MAJOR) {
 		mutex_lock(&ext_devt_mutex);
-		idr_remove(&ext_devt_idr, MINOR(devt));
+		idr_remove(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
 		mutex_unlock(&ext_devt_mutex);
 	}
 }
@@ -473,7 +505,7 @@ struct gendisk *get_gendisk(dev_t devt, int *partno)
 		struct hd_struct *part;
 
 		mutex_lock(&ext_devt_mutex);
-		part = idr_find(&ext_devt_idr, MINOR(devt));
+		part = idr_find(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
 		if (part && get_disk(part_to_disk(part))) {
 			*partno = part->partno;
 			disk = part_to_disk(part);
diff --git a/drivers/ide/ide-disk.c b/drivers/ide/ide-disk.c
index 7a88de9ada2..a072df5053a 100644
--- a/drivers/ide/ide-disk.c
+++ b/drivers/ide/ide-disk.c
@@ -42,7 +42,13 @@
 #include <asm/div64.h>
 
 #define IDE_DISK_PARTS		(1 << PARTN_BITS)
+
+#if !defined(CONFIG_DEBUG_BLOCK_EXT_DEVT)
 #define IDE_DISK_MINORS		IDE_DISK_PARTS
+#else
+#define IDE_DISK_MINORS		1
+#endif
+
 #define IDE_DISK_EXT_MINORS	(IDE_DISK_PARTS - IDE_DISK_MINORS)
 
 struct ide_disk_obj {
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index d1bb0e1d2d2..280d231a86e 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -87,7 +87,13 @@ MODULE_ALIAS_SCSI_DEVICE(TYPE_MOD);
 MODULE_ALIAS_SCSI_DEVICE(TYPE_RBC);
 
 #define SD_PARTS	64
+
+#if !defined(CONFIG_DEBUG_BLOCK_EXT_DEVT)
 #define SD_MINORS	16
+#else
+#define SD_MINORS	1
+#endif
+
 #define SD_EXT_MINORS	(SD_PARTS - SD_MINORS)
 
 static int  sd_revalidate_disk(struct gendisk *);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 0b504814e37..5a536f703a8 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -624,6 +624,22 @@ config BACKTRACE_SELF_TEST
 
 	  Say N if you are unsure.
 
+config DEBUG_BLOCK_EXT_DEVT
+        bool "Force extended block device numbers and spread them"
+	depends on DEBUG_KERNEL
+	depends on BLOCK
+	default y
+	help
+	  Conventionally, block device numbers are allocated from
+	  predetermined contiguous area.  However, extended block area
+	  may introduce non-contiguous block device numbers.  This
+	  option forces most block device numbers to be allocated from
+	  the extended space and spreads them to discover kernel or
+	  userland code paths which assume predetermined contiguous
+	  device number allocation.
+
+	  Say N if you are unsure.
+
 config LKDTM
 	tristate "Linux Kernel Dump Test Tool Module"
 	depends on DEBUG_KERNEL