ovl: fix copy-up in tmpfile

Move ovl_copy_up() call outside of ovl_want_write()/ovl_drop_write()
region, since copy up may also call ovl_want_write() resulting in recursive
locking on sb->s_writers.

Reported-and-tested-by: syzbot+85e58cdf5b3136471d4b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000f6865106191c3e58@google.com/
Fixes: 9a87907 ("ovl: implement tmpfile")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: Miklos Szeredi

fs/overlayfs/dir.c

@@ -1314,10 +1314,6 @@ static int ovl_create_tmpfile(struct file *file, struct dentry *dentry,
 	int flags = file->f_flags | OVL_OPEN_FLAGS;
 	int err;
 
-	err = ovl_copy_up(dentry->d_parent);
-	if (err)
-		return err;
-
 	old_cred = ovl_override_creds(dentry->d_sb);
 	err = ovl_setup_cred_for_create(dentry, inode, mode, old_cred);
 	if (err)
@@ -1360,6 +1356,10 @@ static int ovl_tmpfile(struct mnt_idmap *idmap, struct inode *dir,
 	if (!OVL_FS(dentry->d_sb)->tmpfile)
 		return -EOPNOTSUPP;
 
+	err = ovl_copy_up(dentry->d_parent);
+	if (err)
+		return err;
+
 	err = ovl_want_write(dentry);
 	if (err)
 		return err;