From 821525e5032bf56912ecce5f2aa650c57ea89ea2 Mon Sep 17 00:00:00 2001
From: Mahmoud Al-Qudsi <mqudsi@neosmart.net>
Date: Sat, 30 May 2020 15:59:44 -0500
Subject: [PATCH] Defend against race condition calculating job cpu usage

Closes #7066
---
 src/builtin_jobs.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/builtin_jobs.cpp b/src/builtin_jobs.cpp
index 6b0aa84fb..1dd0a16c2 100644
--- a/src/builtin_jobs.cpp
+++ b/src/builtin_jobs.cpp
@@ -32,13 +32,18 @@ static int cpu_use(const job_t *j) {
 
     for (const process_ptr_t &p : j->processes) {
         struct timeval t;
-        int jiffies;
+        unsigned long jiffies;
         gettimeofday(&t, nullptr);
         jiffies = proc_get_jiffies(p.get());
 
         double t1 = 1000000.0 * p->last_time.tv_sec + p->last_time.tv_usec;
         double t2 = 1000000.0 * t.tv_sec + t.tv_usec;
 
+        // Check for a race condition that can cause negative CPU usage to be reported (#7066)
+        if (t2 < t1 || jiffies < p->last_jiffies) {
+            continue;
+        }
+
         // std::fwprintf( stderr, L"t1 %f t2 %f p1 %d p2 %d\n", t1, t2, jiffies, p->last_jiffies );
         u += (static_cast<double>(jiffies - p->last_jiffies)) / (t2 - t1);
     }