[PATCH] md: Assorted little md fixes

- version-1 superblock
  + The default_bitmap_offset is in sectors, not bytes.
  + the 'size' field in the superblock is in sectors, not KB
- raid0_run should return a negative number on error, not '1'
- raid10_read_balance should not return a valid 'disk' number if
     ->rdev turned out to be NULL
- kmem_cache_destroy doesn't like being passed a NULL.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/md/raid6main.c b/drivers/md/raid6main.c
index ed2abb2..cd477eb 100644
--- a/drivers/md/raid6main.c
+++ b/drivers/md/raid6main.c
@@ -366,7 +366,8 @@
 	while (drop_one_stripe(conf))
 		;
 
-	kmem_cache_destroy(conf->slab_cache);
+	if (conf->slab_cache)
+		kmem_cache_destroy(conf->slab_cache);
 	conf->slab_cache = NULL;
 }