Make cgroup creation/deletion more robust

- Don't attempt to create directory is controller is not
  present in the system
- Ensure that all files being written exist in cgroupfs
- Attempt to delete directories during Uninstall even if
  other deletions have failed

Fixes #6446

PiperOrigin-RevId: 402614820

2 files changed, 59 insertions, 0 deletions

diff --git a/pkg/sync/BUILD b/pkg/sync/BUILD
index 73791b456..517f16329 100644
--- a/pkg/sync/BUILD
+++ b/pkg/sync/BUILD
@@ -26,6 +26,7 @@ go_library(
         "rwmutex_unsafe.go",
         "seqcount.go",
         "sync.go",
+        "wait.go",
     ],
     marshal = False,
     stateify = False,
diff --git a/pkg/sync/wait.go b/pkg/sync/wait.go
new file mode 100644
index 000000000..f8e7742a5
--- /dev/null
+++ b/pkg/sync/wait.go
@@ -0,0 +1,58 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sync
+
+// WaitGroupErr is similar to WaitGroup but allows goroutines to report error.
+// Only the first error is retained and reported back.
+//
+// Example usage:
+// 	wg := WaitGroupErr{}
+// 	wg.Add(1)
+// 	go func() {
+//			defer wg.Done()
+//			if err := ...; err != nil {
+//				wg.ReportError(err)
+//				return
+// 			}
+// 	}()
+//	return wg.Error()
+//
+type WaitGroupErr struct {
+	WaitGroup
+
+	// mu protects firstErr.
+	mu Mutex
+
+	// firstErr holds the first error reported. nil is no error occurred.
+	firstErr error
+}
+
+// ReportError reports an error. Note it does not call Done().
+func (w *WaitGroupErr) ReportError(err error) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if w.firstErr == nil {
+		w.firstErr = err
+	}
+}
+
+// Error waits for the counter to reach 0 and returns the first reported error
+// if any.
+func (w *WaitGroupErr) Error() error {
+	w.Wait()
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	return w.firstErr
+}