From 7699384b0c0ee9a7322b201cbd4ba2284a44c0c9 Mon Sep 17 00:00:00 2001
From: Colin Walters <walters@verbum.org>
Date: Tue, 16 Aug 2022 10:38:28 -0400
Subject: [PATCH] daemon: Add a workaround for bug 2111817

So about a month ago we merged
https://github.com/openshift/machine-config-operator/pull/3239/commits/0bcb4d205d7343436ffdc482f8ede73bc429552a
which dropped all the old workarounds we had for rpm-ostree bugs.

I'm sure you are all shocked that less than a month later, we have
a new one to add in this section.

Actually though one of those previous bugs was arguably really a
systemd bug provoked by rpm-ostree...and that's the case again here.

This is all covered in
https://bugzilla.redhat.com/show_bug.cgi?id=2104619
and
https://github.com/coreos/rpm-ostree/pull/3939/commits/21c82ffe36dff61b2be8778634c571cb177a24e9
but TL;DR systemd's implementation of `InaccessiblePaths` has
quadratic behavior in number of mounts, and so of course
we only discover this when we're testing heavily loaded OCP clusters.

The fix to rpm-ostree is inbound.  But...adding this workaround which
has the MCD dynamically reconfigure the system to drop that config will
help unstick clusters so they can get the real fix.
---
 pkg/daemon/rpm-ostree.go | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/pkg/daemon/rpm-ostree.go b/pkg/daemon/rpm-ostree.go
index 708db4bca5..e64cf96dda 100644
--- a/pkg/daemon/rpm-ostree.go
+++ b/pkg/daemon/rpm-ostree.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 	"time"
 
@@ -105,8 +106,35 @@ func (r *RpmOstreeClient) loadStatus() (*rpmOstreeState, error) {
 	return &rosState, nil
 }
 
+// See https://bugzilla.redhat.com/show_bug.cgi?id=2111817
+func bug2111817Workaround() error {
+	targetUnit := "/run/systemd/system/rpm-ostreed.service.d/bug2111817.conf"
+	// Do nothing if the file exists
+	if _, err := os.Stat(targetUnit); err == nil {
+		return nil
+	}
+	err := os.MkdirAll(filepath.Dir(targetUnit), 0o755)
+	if err != nil {
+		return err
+	}
+	dropin := `[Service]
+InaccessiblePaths=
+`
+	if err := writeFileAtomicallyWithDefaults(targetUnit, []byte(dropin)); err != nil {
+		return err
+	}
+	if err := runCmdSync("systemctl", "daemon-reload"); err != nil {
+		return err
+	}
+	glog.Infof("Enabled workaround for bug 2111817")
+	return nil
+}
+
 func (r *RpmOstreeClient) Initialize() error {
-	// This used to have some workarounds for rpm-ostree bugs, but we no longer need those.
+	if err := bug2111817Workaround(); err != nil {
+		return err
+	}
+
 	return nil
 }