mm: shmem: add missing shmem_unacct_size() in __shmem_file_setup()

We will miss shmem_unacct_size() when is_idmapped_mnt() returns a failure.
Move is_idmapped_mnt() before shmem_acct_size() to fix the issue.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 7a80e5b ("shmem: support idmapped mounts for tmpfs")
Signed-off-by: Kemeng Shi <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: kernel test robot <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Kemeng Shi

mm/shmem.c

@@ -5812,12 +5812,12 @@ static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name,
 	if (size < 0 || size > MAX_LFS_FILESIZE)
 		return ERR_PTR(-EINVAL);
 
-	if (shmem_acct_size(flags, size))
-		return ERR_PTR(-ENOMEM);
-
 	if (is_idmapped_mnt(mnt))
 		return ERR_PTR(-EINVAL);
 
+	if (shmem_acct_size(flags, size))
+		return ERR_PTR(-ENOMEM);
+
 	inode = shmem_get_inode(&nop_mnt_idmap, mnt->mnt_sb, NULL,
 				S_IFREG | S_IRWXUGO, 0, flags);
 	if (IS_ERR(inode)) {