Bug 1790611 - Add a high priority NotifyShutdownSuccess that avoids blaming the content process with a dump. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D157292

dom/ipc/ContentChild.cpp

@@ -3055,9 +3055,9 @@ void ContentChild::ShutdownInternal() {
     SendShutdownPerfStats(PerfStats::CollectLocalPerfStatsJSON());
   }
 
-  // Start a timer that will insure we quickly exit after a reasonable
-  // period of time. Prevents shutdown hangs after our connection to the
-  // parent closes.
+  // Start a timer that will ensure we quickly exit after a reasonable period
+  // of time. Prevents shutdown hangs after our connection to the parent
+  // closes or when the parent is too busy to ever kill us.
   CrashReporter::AppendToCrashReportAnnotation(
       CrashReporter::Annotation::IPCShutdownState, "StartForceKillTimer"_ns);
   StartForceKillTimer();
@@ -3065,7 +3065,16 @@ void ContentChild::ShutdownInternal() {
   CrashReporter::AppendToCrashReportAnnotation(
       CrashReporter::Annotation::IPCShutdownState,
       "SendFinishShutdown (sending)"_ns);
+
+  // Notify the parent that we are done with shutdown. This is sent with high
+  // priority and will just flag we are done.
+  Unused << SendNotifyShutdownSuccess();
+
+  // Now tell the parent to actually destroy our channel which will make end
+  // our process. This is expected to be the last event the parent will
+  // ever process for this ContentChild.
   bool sent = SendFinishShutdown();
+
   CrashReporter::AppendToCrashReportAnnotation(
       CrashReporter::Annotation::IPCShutdownState,
       sent ? "SendFinishShutdown (sent)"_ns : "SendFinishShutdown (failed)"_ns);

dom/ipc/ContentParent.cpp

@@ -1855,11 +1855,24 @@ void ContentParent::ShutDownProcess(ShutDownMethod aMethod) {
   ShutDownMessageManager();
 }
 
+mozilla::ipc::IPCResult ContentParent::RecvNotifyShutdownSuccess() {
+  if (!mShutdownPending) {
+    return IPC_FAIL(this, "RecvNotifyShutdownSuccess without mShutdownPending");
+  }
+
+  mIsNotifiedShutdownSuccess = true;
+
+  return IPC_OK();
+}
+
 mozilla::ipc::IPCResult ContentParent::RecvFinishShutdown() {
+  if (!mShutdownPending) {
+    return IPC_FAIL(this, "RecvFinishShutdown without mShutdownPending");
+  }
+
   // At this point, we already called ShutDownProcess once with
   // SEND_SHUTDOWN_MESSAGE. To actually close the channel, we call
   // ShutDownProcess again with CLOSE_CHANNEL.
-  MOZ_ASSERT(mShutdownPending);
   if (mCalledClose) {
     MaybeLogBlockShutdownDiagnostics(
         this, "RecvFinishShutdown: Channel already closed.", __FILE__,
@@ -4318,10 +4331,16 @@ void ContentParent::KillHard(const char* aReason) {
   mForceKillTimer = nullptr;
 
   RemoveShutdownBlockers();
+  nsCString reason = nsDependentCString(aReason);
 
-  GeneratePairedMinidump(aReason);
-
-  nsDependentCString reason(aReason);
+  // If we find mIsNotifiedShutdownSuccess there is no reason to blame this
+  // content process, most probably our parent process is just slow in
+  // processing its own main thread queue.
+  if (!mIsNotifiedShutdownSuccess) {
+    GeneratePairedMinidump(aReason);
+  } else {
+    reason = nsDependentCString("KillHard after IsNotifiedShutdownSuccess.");
+  }
   Telemetry::Accumulate(Telemetry::SUBPROCESS_KILL_HARD, reason, 1);
 
   ProcessHandle otherProcessHandle;

dom/ipc/ContentParent.h

@@ -469,6 +469,8 @@ class ContentParent final : public PContentParent,
 
   mozilla::ipc::IPCResult RecvFinishShutdown();
 
+  mozilla::ipc::IPCResult RecvNotifyShutdownSuccess();
+
   void MaybeInvokeDragSession(BrowserParent* aParent);
 
   PContentPermissionRequestParent* AllocPContentPermissionRequestParent(
@@ -1645,6 +1647,8 @@ class ContentParent final : public PContentParent,
 
   static uint32_t sMaxContentProcesses;
   static Maybe<TimeStamp> sLastContentProcessLaunch;
+
+  bool mIsNotifiedShutdownSuccess = false;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(ContentParent, NS_CONTENTPARENT_IID)

dom/ipc/PContent.ipdl

@@ -1285,6 +1285,11 @@ parent:
 
     async RequestAnonymousTemporaryFile(uint64_t aID);
 
+    /**
+     * Notifies the parent that the child needs no more ForceKill dump.
+     */
+    [Priority=control] async NotifyShutdownSuccess();
+
     /**
      * Notifies the parent to continue shutting down after the child performs
      * its shutdown tasks.