[PATCH v2] ubifs: Fix reference count leak in ubifsumount

["Pali Rohár" <pali@kernel.org>]

Original ubifs code was designed that after ubifs_umount() call it is
required to also call ubi_close_volume() which closes underlying UBI
volume. But U-Boot ubifs modification have not implemented it properly
which caused that ubifsumount command contains resource leak. It can be
observed by calling simple sequence of commands:

  => ubi part mtd2
  ubi0: attaching mtd2
  ...
  => ubifsmount ubi0
  => ubifsumount
  Unmounting UBIFS volume rootfs!
  => ubi detach
  ubi0 error: ubi_detach_mtd_dev: ubi0 reference count 1, destroy anyway
  ubi0: detaching mtd2
  ubi0: mtd2 is detached

Fix this issue by calling ubi_close_volume() and mutex_unlock() in
directly in ubifs_umount() function before freeing U-Boot's global
ubifs_sb. And remove duplicate calls of these two functions in remaining
places. Note that when ubifs_umount() is not called then during error
handling is still needed to call ubi_close_volume() and mutex_unlock.

With this change ubifsumount command does not throw that error anymore:

  => ubi part rootfs
  ubi0: attaching mtd2
  ...
  => ubifsmount ubi0
  => ubifsumount
  Unmounting UBIFS volume rootfs!
  => ubi detach
  ubi0: detaching mtd2
  ubi0: mtd2 is detached

Signed-off-by: Pali Rohár <pali@kernel.org>
---
Changes in v2:
* Fix error handling in ubifs_fill_super()
---
 fs/ubifs/super.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index e3a4c0bca270..034c41a70356 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -1757,6 +1757,8 @@ void ubifs_umount(struct ubifs_info *c)
 	kfree(c->bottom_up_buf);
 	ubifs_debugging_exit(c);
 #ifdef __UBOOT__
+	ubi_close_volume(c->ubi);
+	mutex_unlock(&c->umount_mutex);
 	/* Finally free U-Boot's global copy of superblock */
 	if (ubifs_sb != NULL) {
 		free(ubifs_sb->s_fs_info);
@@ -2058,9 +2060,9 @@ static void ubifs_put_super(struct super_block *sb)
 	ubifs_umount(c);
 #ifndef __UBOOT__
 	bdi_destroy(&c->bdi);
-#endif
 	ubi_close_volume(c->ubi);
 	mutex_unlock(&c->umount_mutex);
+#endif
 }
 #endif
 
@@ -2327,6 +2329,9 @@ static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
 
 out_umount:
 	ubifs_umount(c);
+#ifdef __UBOOT__
+	goto out;
+#endif
 out_unlock:
 	mutex_unlock(&c->umount_mutex);
 #ifndef __UBOOT__
-- 
2.20.1