[PATCH] fix for get_sb_bdev() bug

[Alexander Viro]

	Grr...  When loop in get_sb_bdev() had been switched from
global list of superblock to per-type one, we should have switched
from sb_entry(p) (aka. list_entry(p, struct super_block, s_list)) to
list_entry(p, struct super_block, s_instances).

	As it is, we end up with false negatives all the time.  I.e.
second mount from the same block device with the same type gices
a new superblock.  With obvious nasty results...

	Patch below fixes that.

--- C6-0/fs/super.c	Fri Mar  8 19:01:07 2002
+++ C6-0/fs/super.c.fix	Mon Mar 11 01:22:26 2002
@@ -728,7 +728,8 @@
 	spin_lock(&sb_lock);
 
 	list_for_each(p, &fs_type->fs_supers) {
-		struct super_block *old = sb_entry(p);
+		struct super_block *old;
+		old = list_entry(p, struct super_block, s_instances);
 		if (old->s_bdev != bdev)
 			continue;
 		if (!grab_super(old))