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 <anton@samba.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -624,10 +624,8 @@ int setup_arg_pages(struct linux_binprm *bprm,
 	/* 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
@@ -641,7 +639,7 @@ int setup_arg_pages(struct linux_binprm *bprm,
 
 out_unlock:
 	up_write(&mm->mmap_sem);
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL(setup_arg_pages);