Merged PR 732965: Kill active ptracerunners on SandboxedProcess.KillAsync

Related work items: #2075989

Author: pgunasekara

Diff for: Public/Src/Engine/Processes/SandboxedProcessUnix.cs

@@ -429,6 +429,8 @@ protected override async Task KillAsyncInternal(bool dumpProcessTree)
             {
                 // surviving child processes may only be set when the process is explicitly killed
                 m_survivingChildProcesses = NullIfEmpty(CoalesceProcesses(GetCurrentlyActiveChildProcesses()));
+                // Before notifying that the root process has exited, kill all ptracerunners to avoid receiving access reports after the communication pipe is closed.
+                KillActivePTraceRunners();
                 await base.KillAsyncInternal(dumpProcessTree);
                 KillAllChildProcesses();
                 SandboxConnection.NotifyRootProcessExited(PipId, this);
@@ -499,11 +501,7 @@ public override void Dispose()
 
             // If ptrace runners have not finished yet, then do that now
             // Completing the task below will make us kill any leftover PTraceRunner processes
-            m_ptraceRunnersCancellation.SetResult(true);
-            foreach (var runner in TaskUtilities.SafeWhenAll(m_ptraceRunners.ToArray()).GetAwaiter().GetResult())
-            {
-                runner.Dispose();
-            }
+            KillActivePTraceRunners();
 
             base.Dispose();
         }
@@ -1130,5 +1128,17 @@ async Task<AsyncProcessExecutor> runnerTask(AsyncProcessExecutor runner)
                 return runner;
             }
         }
+
+        private void KillActivePTraceRunners()
+        {
+            var ptraceRunners = m_ptraceRunners.ToArray();
+            m_ptraceRunners.Clear();
+
+            m_ptraceRunnersCancellation.TrySetResult(true);
+            foreach (var runner in TaskUtilities.SafeWhenAll(ptraceRunners).GetAwaiter().GetResult())
+            {
+                runner.Dispose();
+            }
+        }
     }
 }