[PATCH] sysfs: sysfs_remove_dir() needs to invalidate the dentry

When calling sysfs_remove_dir() don't allow any further sysfs functions
to work for this kobject anymore.  This fixes a nasty USB cdc-acm oops
on disconnect.

Many thanks to Bob Copeland and Paul Fulghum for taking the time to
track this down.

Cc: Bob Copeland <email@bobcopeland.com>
Cc: Paul Fulghum <paulkf@microgate.com>
Cc: Maneesh Soni <maneesh@in.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 49bd219..cfd290d 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -302,6 +302,7 @@
 	 * Drop reference from dget() on entrance.
 	 */
 	dput(dentry);
+	kobj->dentry = NULL;
 }
 
 int sysfs_rename_dir(struct kobject * kobj, const char *new_name)