sysfs: remove BUG_ON() from sysfs_remove_group()

It's possible that the caller of sysfs_remove_group messed up and passed in an attribute group that was not really registered to this kobject.  But don't panic for such a foolish error, spit out a warning about what happened, and continue on our way safely.

Cc: Roland Dreier <rdreier@cisco.com>
Cc: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/sysfs/group.c

@@ -77,7 +77,12 @@ void sysfs_remove_group(struct kobject * kobj,
 
 	if (grp->name) {
 		sd = sysfs_get_dirent(dir_sd, grp->name);
-		BUG_ON(!sd);
+		if (!sd) {
+			printk(KERN_WARNING "sysfs group %p not found for "
+				"kobject '%s'\n", grp, kobject_name(kobj));
+			WARN_ON(!sd);
+			return;
+		}
 	} else
 		sd = sysfs_get(dir_sd);