From 7030d2e44fccc6c0fc5f5bc87eb05d7134744131 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B6rg=20Thalheim?= <joerg@thalheim.io>
Date: Sat, 3 May 2025 13:28:57 +0200
Subject: [PATCH] cgroups: reapp child processes before destroying cgroup

killing is enough to destroy a cgroup, we need to remove the wait state
of zombie processes before we can destroy the cgroup.
---
 src/libutil/linux/cgroup.cc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/libutil/linux/cgroup.cc b/src/libutil/linux/cgroup.cc
index 4acfe82f1..ae90565a9 100644
--- a/src/libutil/linux/cgroup.cc
+++ b/src/libutil/linux/cgroup.cc
@@ -8,6 +8,7 @@
 #include <cmath>
 #include <regex>
 #include <unordered_set>
+#include <sys/wait.h>
 #include <thread>
 
 #include <dirent.h>
@@ -101,6 +102,11 @@ static CgroupStats destroyCgroup(const std::filesystem::path & cgroup, bool retu
             // FIXME: pid wraparound
             if (kill(pid, SIGKILL) == -1 && errno != ESRCH)
                 throw SysError("killing member %d of cgroup '%s'", pid, cgroup);
+
+            while (waitpid(pid, nullptr, 0) == -1) {
+                if (errno == ECHILD) break; // Process already reaped
+                if (errno != EINTR) throw SysError("waiting for pid %d", pid);
+            }
         }
 
         auto sleep = std::chrono::milliseconds((int) std::pow(2.0, std::min(round, 10)));