do_last(): simplify the liveness analysis past finish_open_created

Don't mess with got_write there - it is guaranteed to be false on
entry and it will be set true if and only if we decide to go for
truncation and manage to get write access for that.

Don't carry acc_mode through the entire thing - it's only used
in that part.  And don't bother with gotos in there - compiler is
quite capable of optimizing that.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -3122,9 +3122,9 @@ static const char *do_last(struct nameidata *nd,
 	kuid_t dir_uid = nd->inode->i_uid;
 	umode_t dir_mode = nd->inode->i_mode;
 	int open_flag = op->open_flag;
-	bool will_truncate = (open_flag & O_TRUNC) != 0;
+	bool do_truncate;
 	bool got_write = false;
-	int acc_mode = op->acc_mode;
+	int acc_mode;
 	unsigned seq;
 	struct inode *inode;
 	struct dentry *dentry;
@@ -3243,36 +3243,30 @@ static const char *do_last(struct nameidata *nd,
 		return ERR_PTR(-ENOTDIR);
 
 finish_open_created:
+	do_truncate = false;
+	acc_mode = op->acc_mode;
 	if (file->f_mode & FMODE_CREATED) {
 		/* Don't check for write permission, don't truncate */
 		open_flag &= ~O_TRUNC;
-		will_truncate = false;
 		acc_mode = 0;
-	} else if (!d_is_reg(nd->path.dentry)) {
-		will_truncate = false;
-	}
-	if (will_truncate) {
+	} else if (d_is_reg(nd->path.dentry) && open_flag & O_TRUNC) {
 		error = mnt_want_write(nd->path.mnt);
 		if (error)
 			return ERR_PTR(error);
-		got_write = true;
+		do_truncate = true;
 	}
 	error = may_open(&nd->path, acc_mode, open_flag);
-	if (error)
-		goto out;
-	if (!(file->f_mode & FMODE_OPENED))
+	if (!error && !(file->f_mode & FMODE_OPENED))
 		error = vfs_open(&nd->path, file);
-	if (error)
-		goto out;
-	error = ima_file_check(file, op->acc_mode);
-	if (!error && will_truncate)
+	if (!error)
+		error = ima_file_check(file, op->acc_mode);
+	if (!error && do_truncate)
 		error = handle_truncate(file);
-out:
 	if (unlikely(error > 0)) {
 		WARN_ON(1);
 		error = -EINVAL;
 	}
-	if (got_write)
+	if (do_truncate)
 		mnt_drop_write(nd->path.mnt);
 	return ERR_PTR(error);
 }