From 00309eea27470b140b9d5998dbe21fbb0946d2a8 Mon Sep 17 00:00:00 2001
From: James Addison <jay@jp-hosting.net>
Date: Mon, 25 Jan 2021 15:30:03 +0000
Subject: [PATCH] src: read exactly two tokens from Linux THP sysfs config

There was an unexpected and hard-to-spot issue here:
the /sys/kernel/mm/transparent_hugepage/enabled file contains three
entries, and the std::ifstream reader was reading two values on each
loop iteration, resulting in incorrect behaviour.

Fixes: https://github.com/nodejs/node/issues/37064

PR-URL: https://github.com/nodejs/node/pull/37065
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
---
 src/large_pages/node_large_page.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/large_pages/node_large_page.cc b/src/large_pages/node_large_page.cc
index a4b109d1b0ef69..22810ef08fb878 100644
--- a/src/large_pages/node_large_page.cc
+++ b/src/large_pages/node_large_page.cc
@@ -260,6 +260,8 @@ struct text_region FindNodeTextRegion() {
 bool IsTransparentHugePagesEnabled() {
   std::ifstream ifs;
 
+  // File format reference:
+  // https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/huge_memory.c?id=13391c60da3308ed9980de0168f74cce6c62ac1d#n163
   ifs.open("/sys/kernel/mm/transparent_hugepage/enabled");
   if (!ifs) {
     PrintWarning("could not open /sys/kernel/mm/transparent_hugepage/enabled");
@@ -268,7 +270,7 @@ bool IsTransparentHugePagesEnabled() {
 
   std::string always, madvise;
   if (ifs.is_open()) {
-    while (ifs >> always >> madvise) {}
+    ifs >> always >> madvise;
   }
   ifs.close();