sysfs: In sysfs_chmod_file lazily propagate the mode change.

Now that sysfs_getattr and sysfs_permission refresh the vfs
inode there is no need to immediatly push the mode change
into the vfs cache.  Reducing the amount of work needed and
simplifying the locking.
Acked-by: NTejun Heo <tj@kernel.org>
Acked-by: NSerge Hallyn <serue@us.ibm.com>
Signed-off-by: NEric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

fs/sysfs/file.c

@@ -579,38 +579,23 @@ EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);
  */
 int sysfs_chmod_file(struct kobject *kobj, struct attribute *attr, mode_t mode)
 {
-	struct sysfs_dirent *victim_sd = NULL;
-	struct dentry *victim = NULL;
-	struct inode * inode;
+	struct sysfs_dirent *sd;
 	struct iattr newattrs;
 	int rc;
 
-	rc = -ENOENT;
-	victim_sd = sysfs_get_dirent(kobj->sd, attr->name);
-	if (!victim_sd)
-		goto out;
+	mutex_lock(&sysfs_mutex);
 
-	mutex_lock(&sysfs_rename_mutex);
-	victim = sysfs_get_dentry(victim_sd);
-	mutex_unlock(&sysfs_rename_mutex);
-	if (IS_ERR(victim)) {
-		rc = PTR_ERR(victim);
-		victim = NULL;
+	rc = -ENOENT;
+	sd = sysfs_find_dirent(kobj->sd, attr->name);
+	if (!sd)
 		goto out;
-	}
-
-	inode = victim->d_inode;
 
-	mutex_lock(&inode->i_mutex);
-
-	newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
+	newattrs.ia_mode = (mode & S_IALLUGO) | (sd->s_mode & ~S_IALLUGO);
 	newattrs.ia_valid = ATTR_MODE;
-	rc = sysfs_setattr(victim, &newattrs);
+	rc = sysfs_sd_setattr(sd, &newattrs);
 
-	mutex_unlock(&inode->i_mutex);
  out:
-	dput(victim);
-	sysfs_put(victim_sd);
+	mutex_unlock(&sysfs_mutex);
 	return rc;
 }
 EXPORT_SYMBOL_GPL(sysfs_chmod_file);