From 3f54a80824cca1dc00a2c500e13716df09740b95 Mon Sep 17 00:00:00 2001
From: christoph-zededa <121871801+christoph-zededa@users.noreply.github.com>
Date: Wed, 25 Jun 2025 20:59:47 +0200
Subject: [PATCH] git: synchronize `update-index` with a mutex (#4130)

if `pkglib.NewFromConfig` is used in parallel, it calls
```
git -C /some/directory update-index -q --refresh
```
in parallel.

But `git` does not like this and exits with 128.

This can be easily tried with:
```
git -C /some/dir update-index -q --refresh & \
git -C /some/dir update-index -q --refresh
```

Signed-off-by: Christoph Ostarek <christoph@zededa.com>
---
 src/cmd/linuxkit/pkglib/git.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/cmd/linuxkit/pkglib/git.go b/src/cmd/linuxkit/pkglib/git.go
index 8d65ef802..a953e91b3 100644
--- a/src/cmd/linuxkit/pkglib/git.go
+++ b/src/cmd/linuxkit/pkglib/git.go
@@ -12,6 +12,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"strings"
+	"sync"
 
 	log "github.com/sirupsen/logrus"
 )
@@ -27,6 +28,8 @@ type git struct {
 	dir string
 }
 
+var gitMutex sync.Mutex
+
 // Returns git==nil and no error if the path is not within a git repository
 func newGit(dir string) (*git, error) {
 	g := &git{dir}
@@ -190,9 +193,12 @@ func (g git) isDirty(pkg, commit string) (bool, error) {
 	// because `git diff-index` only uses the `lstat` result and
 	// not the actual file contents. Running `git update-index
 	// --refresh` updates the cache.
+	gitMutex.Lock()
 	if err := g.command("update-index", "-q", "--refresh"); err != nil {
+		gitMutex.Unlock()
 		return false, err
 	}
+	gitMutex.Unlock()
 
 	// diff-index works pretty well, except that
 	err := g.command("diff-index", "--quiet", commit, "--", pkg)