try to fix root ownership

runner/limiter_linux.go

@@ -17,6 +17,7 @@ import (
 var (
 	cgroupRootOnce  sync.Once
 	cgroupRoot      string
+	cgroupRootOwned bool
 	cgroupInitErr   error
 	cgroupCounter   int64
 )
@@ -25,10 +26,80 @@ const cgroupFSRoot = "/sys/fs/cgroup"
 
 func ensureCgroupRoot() (string, error) {
 	cgroupRootOnce.Do(func() {
+		if root, err := createOwnedCgroup(); err == nil {
+			cgroupRoot = root
+			cgroupRootOwned = true
+			return
+		}
+
+		root, err := createScopeCgroup()
+		if err != nil {
+			cgroupInitErr = err
+			return
+		}
+		cgroupRoot = root
+	})
+	return cgroupRoot, cgroupInitErr
+}
+
+func hasController(path, name string) (bool, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return false, err
+	}
+	needle := " " + name + " "
+	return strings.Contains(" "+strings.TrimSpace(string(data))+" ", needle), nil
+}
+
+func createOwnedCgroup() (string, error) {
+	ok, err := hasController(filepath.Join(cgroupFSRoot, "cgroup.controllers"), "memory")
+	if err != nil {
+		return "", err
+	}
+	if !ok {
+		return "", fmt.Errorf("memory controller not available in root cgroup")
+	}
+
+	enabled, err := hasController(filepath.Join(cgroupFSRoot, "cgroup.subtree_control"), "memory")
+	if err != nil {
+		return "", err
+	}
+	if !enabled {
+		if err := os.WriteFile(filepath.Join(cgroupFSRoot, "cgroup.subtree_control"), []byte("+memory"), 0644); err != nil {
+			return "", fmt.Errorf("enable +memory in root subtree_control: %w", err)
+		}
+	}
+
+	name := fmt.Sprintf("judge.%d", os.Getpid())
+	root := filepath.Join(cgroupFSRoot, name)
+	if err := os.Mkdir(root, 0755); err != nil {
+		if os.IsExist(err) {
+		} else {
+			return "", err
+		}
+	}
+
+	ok, err = hasController(filepath.Join(root, "cgroup.controllers"), "memory")
+	if err != nil {
+		_ = os.Remove(root)
+		return "", err
+	}
+	if !ok {
+		_ = os.Remove(root)
+		return "", fmt.Errorf("memory controller not inherited into %s", root)
+	}
+	if err := os.WriteFile(filepath.Join(root, "cgroup.subtree_control"), []byte("+memory"), 0644); err != nil {
+		_ = os.Remove(root)
+		return "", fmt.Errorf("enable +memory in %s: %w", root, err)
+	}
+
+	return root, nil
+}
+
+func createScopeCgroup() (string, error) {
 	data, err := os.ReadFile("/proc/self/cgroup")
 	if err != nil {
-			cgroupInitErr = fmt.Errorf("read /proc/self/cgroup: %w", err)
-			return
+		return "", fmt.Errorf("read /proc/self/cgroup: %w", err)
 	}
 	var rel string
 	for _, line := range strings.Split(strings.TrimSpace(string(data)), "\n") {
@@ -38,42 +109,42 @@ func ensureCgroupRoot() (string, error) {
 		}
 	}
 	if rel == "" {
-			cgroupInitErr = fmt.Errorf("cgroup v2 not found in /proc/self/cgroup (unified hierarchy required)")
-			return
+		return "", fmt.Errorf("cgroup v2 not found in /proc/self/cgroup (unified hierarchy required)")
 	}
 	ownCg := filepath.Join(cgroupFSRoot, rel)
 
-		controllers, err := os.ReadFile(filepath.Join(ownCg, "cgroup.controllers"))
+	ok, err := hasController(filepath.Join(ownCg, "cgroup.controllers"), "memory")
 	if err != nil {
-			cgroupInitErr = fmt.Errorf("cgroup %s not accessible: %w", ownCg, err)
-			return
+		return "", fmt.Errorf("cgroup %s not accessible: %w", ownCg, err)
 	}
-		if !strings.Contains(" "+string(controllers)+" ", " memory ") {
-			cgroupInitErr = fmt.Errorf("memory controller not delegated to %s (controllers: %s)", ownCg, strings.TrimSpace(string(controllers)))
-			return
+	if !ok {
+		return "", fmt.Errorf("memory controller not delegated to %s", ownCg)
 	}
 
 	initCg := filepath.Join(ownCg, "judge.init")
 	if err := os.MkdirAll(initCg, 0755); err != nil {
-			cgroupInitErr = fmt.Errorf("mkdir %s: %w", initCg, err)
-			return
+		return "", fmt.Errorf("mkdir %s: %w", initCg, err)
 	}
 	if err := os.WriteFile(filepath.Join(initCg, "cgroup.procs"), []byte(strconv.Itoa(os.Getpid())), 0644); err != nil {
-			cgroupInitErr = fmt.Errorf("move judge into %s: %w", initCg, err)
-			return
+		return "", fmt.Errorf("move judge into %s: %w", initCg, err)
 	}
 
 	if err := os.WriteFile(filepath.Join(ownCg, "cgroup.subtree_control"), []byte("+memory"), 0644); err != nil {
-			current, _ := os.ReadFile(filepath.Join(ownCg, "cgroup.subtree_control"))
-			if !strings.Contains(" "+string(current)+" ", " memory ") {
-				cgroupInitErr = fmt.Errorf("enable +memory in %s/cgroup.subtree_control: %w", ownCg, err)
-				return
+		enabled, _ := hasController(filepath.Join(ownCg, "cgroup.subtree_control"), "memory")
+		if !enabled {
+			return "", fmt.Errorf("enable +memory in %s/cgroup.subtree_control: %w", ownCg, err)
 		}
 	}
+	return ownCg, nil
+}
 
-		cgroupRoot = ownCg
-	})
-	return cgroupRoot, cgroupInitErr
+func cleanupCgroupRoot() {
+	if cgroupRoot == "" || !cgroupRootOwned {
+		return
+	}
+	_ = os.Remove(cgroupRoot)
+	cgroupRoot = ""
+	cgroupRootOwned = false
 }
 
 type linuxLimiter struct {

runner/limiter_other.go

@@ -25,3 +25,5 @@ func (l *noopLimiter) prepare(cmd *exec.Cmd) error {
 func (l *noopLimiter) afterStart(cmd *exec.Cmd) error { return nil }
 func (l *noopLimiter) collect() limitStats            { return limitStats{} }
 func (l *noopLimiter) cleanup()                       {}
+
+func cleanupCgroupRoot() {}

runner/limiter_windows.go

@@ -132,3 +132,5 @@ func (l *windowsLimiter) cleanup() {
 		l.job = 0
 	}
 }
+
+func cleanupCgroupRoot() {}

runner/runner.go

@@ -59,6 +59,8 @@ func resolveBinary(workDir, name string) string {
 }
 
 func (r *Runner) Run() *SuiteResult {
+	defer cleanupCgroupRoot()
+
 	result := &SuiteResult{}
 
 	buildLog, err := r.build()