exec: setup_arg_pages() fails to return errors

In setup_arg_pages we work hard to assign a value to ret, but on exit we
always return 0.

Also remove a now duplicated exit path and branch to out_unlock instead.

Signed-off-by: Anton Blanchard <[e-mail]>
Acked-by: Serge Hallyn <[e-mail]>
Reviewed-by: WANG Cong <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/exec.c

···
 	/* Move stack pages down in memory. */
 	if (stack_shift) {
 		ret = shift_arg_pages(vma, stack_shift);
-		if (ret) {
-			up_write(&mm->mmap_sem);
-			return ret;
-		}
+		if (ret)
+			goto out_unlock;
 	}
 
 #ifdef CONFIG_STACK_GROWSUP
···
 
 out_unlock:
 	up_write(&mm->mmap_sem);
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL(setup_arg_pages);