From 5f56d7426a19016706e8da72ce74bcb5a2a0a198 Mon Sep 17 00:00:00 2001
From: Ben Noordhuis <info@bnoordhuis.nl>
Date: Mon, 8 Jun 2020 13:12:43 +0200
Subject: [PATCH] linux: read load average from /proc/loadavg

It was reported that uv_loadavg() reports the wrong values inside an
lxc container.

Libuv calls sysinfo(2) but that isn't intercepted by lxc. /proc/loadavg
however is because /proc is a FUSE fs inside the container.

This commit makes libuv try /proc/loadavg first and fall back to
sysinfo(2) in case /proc isn't mounted.

This commit is very similar to commit 3a1be725 ("linux: read free/total
memory from /proc/meminfo") from April 2019.

Fixes: https://github.com/nodejs/node/issues/33791
---
 CMakeLists.txt        |  6 ++----
 Makefile.am           |  6 ++----
 src/unix/linux-core.c | 17 +++++++++++++++++
 3 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a44e953c471..cb79bfa3fe8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -192,8 +192,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Android")
        src/unix/pthread-fixes.c
        src/unix/random-getentropy.c
        src/unix/random-getrandom.c
-       src/unix/random-sysctl-linux.c
-       src/unix/sysinfo-loadavg.c)
+       src/unix/random-sysctl-linux.c)
 endif()
 
 if(APPLE OR CMAKE_SYSTEM_NAME MATCHES "Android|Linux|OS390")
@@ -237,8 +236,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
        src/unix/linux-syscalls.c
        src/unix/procfs-exepath.c
        src/unix/random-getrandom.c
-       src/unix/random-sysctl-linux.c
-       src/unix/sysinfo-loadavg.c)
+       src/unix/random-sysctl-linux.c)
 endif()
 
 if(CMAKE_SYSTEM_NAME STREQUAL "NetBSD")
diff --git a/Makefile.am b/Makefile.am
index d9d2f3d02f5..c3391c2a82c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -386,8 +386,7 @@ libuv_la_SOURCES += src/unix/android-ifaddrs.c \
                     src/unix/procfs-exepath.c \
                     src/unix/pthread-fixes.c \
                     src/unix/random-getrandom.c \
-                    src/unix/random-sysctl-linux.c \
-                    src/unix/sysinfo-loadavg.c
+                    src/unix/random-sysctl-linux.c
 endif
 
 if CYGWIN
@@ -468,8 +467,7 @@ libuv_la_SOURCES += src/unix/linux-core.c \
                     src/unix/procfs-exepath.c \
                     src/unix/proctitle.c \
                     src/unix/random-getrandom.c \
-                    src/unix/random-sysctl-linux.c \
-                    src/unix/sysinfo-loadavg.c
+                    src/unix/random-sysctl-linux.c
 test_run_tests_LDFLAGS += -lutil
 endif
 
diff --git a/src/unix/linux-core.c b/src/unix/linux-core.c
index 4148a4f5470..7e5c78c6752 100644
--- a/src/unix/linux-core.c
+++ b/src/unix/linux-core.c
@@ -1084,3 +1084,20 @@ uint64_t uv_get_constrained_memory(void) {
    */
   return uv__read_cgroups_uint64("memory", "memory.limit_in_bytes");
 }
+
+
+void uv_loadavg(double avg[3]) {
+  struct sysinfo info;
+  char buf[128];  /* Large enough to hold all of /proc/loadavg. */
+
+  if (0 == uv__slurp("/proc/loadavg", buf, sizeof(buf)))
+    if (3 == sscanf(buf, "%lf %lf %lf", &avg[0], &avg[1], &avg[2]))
+      return;
+
+  if (sysinfo(&info) < 0)
+    return;
+
+  avg[0] = (double) info.loads[0] / 65536.0;
+  avg[1] = (double) info.loads[1] / 65536.0;
+  avg[2] = (double) info.loads[2] / 65536.0;
+}