ext4: unregister features interface on module unload

Ext4 features interface was not properly unregistered which led to
problems while unloading/reloading ext4 module. This commit fixes that by
adding proper kobject unregistration code into ext4_exit_fs() as well as
fail-path of ext4_init_fs()

Reported-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

fs/ext4/super.c

@@ -4769,7 +4769,7 @@ static struct file_system_type ext4_fs_type = {
 	.fs_flags	= FS_REQUIRES_DEV,
 };
 
-int __init ext4_init_feat_adverts(void)
+static int __init ext4_init_feat_adverts(void)
 {
 	struct ext4_features *ef;
 	int ret = -ENOMEM;
@@ -4793,6 +4793,13 @@ out:
 	return ret;
 }
 
+static void ext4_exit_feat_adverts(void)
+{
+	kobject_put(&ext4_feat->f_kobj);
+	wait_for_completion(&ext4_feat->f_kobj_unregister);
+	kfree(ext4_feat);
+}
+
 static int __init ext4_init_fs(void)
 {
 	int err;
@@ -4839,7 +4846,7 @@ out1:
 out2:
 	ext4_exit_mballoc();
 out3:
-	kfree(ext4_feat);
+	ext4_exit_feat_adverts();
 	remove_proc_entry("fs/ext4", NULL);
 	kset_unregister(ext4_kset);
 out4:
@@ -4858,6 +4865,7 @@ static void __exit ext4_exit_fs(void)
 	destroy_inodecache();
 	ext4_exit_xattr();
 	ext4_exit_mballoc();
+	ext4_exit_feat_adverts();
 	remove_proc_entry("fs/ext4", NULL);
 	kset_unregister(ext4_kset);
 	ext4_exit_system_zone();