Bug 1868304 - Add temporary code in Nightly to diagnose SetReservedClientInfo assertion. r=pbone,dom-worker-reviewers,asuth

To help investigate the crash in bug 1761208, this patch adds code to
register the top frames of the call stack when reservedClientInfo is
set, such that it can be recovered from crash dumps.

We only add this code for Nightly Windows x64 builds because we get a
Nightly crash on this assertion for almost every Nightly build, always
coming from Windows x64. So this should be enough and there is no need
to impact other builds.

This code only needs to live for a few Nightly builds and can/should be
removed once we have caught the faulty call stack.

Differential Revision: https://phabricator.services.mozilla.com/D195525

Author: yjugl

netwerk/base/LoadInfo.cpp

@@ -22,6 +22,7 @@
 #include "mozilla/dom/WindowGlobalParent.h"
 #include "mozilla/net/CookieJarSettings.h"
 #include "mozilla/NullPrincipal.h"
+#include "mozilla/StackWalk.h"
 #include "mozilla/StaticPrefs_network.h"
 #include "mozilla/StaticPrefs_security.h"
 #include "mozIThirdPartyUtil.h"
@@ -50,6 +51,23 @@ using namespace mozilla::dom;
 
 namespace mozilla::net {
 
+#if defined(NIGHTLY_BUILD) && defined(XP_WIN) && defined(_M_X64)
+/* static */ void LoadInfo::StackTrace::StackWalkCallback(uint32_t aFrameNumber,
+                                                          void* aPc, void* aSp,
+                                                          void* aClosure) {
+  StackTrace* st = (StackTrace*)aClosure;
+  MOZ_ASSERT(st->mLength < kMaxFrames);
+  st->mPcs[st->mLength] = aPc;
+  st->mLength++;
+  MOZ_ASSERT(st->mLength == aFrameNumber);
+}
+
+void LoadInfo::StackTrace::Fill() {
+  mLength = 0;
+  MozStackWalk(StackWalkCallback, nullptr, kMaxFrames, this);
+}
+#endif  // NIGHTLY_BUILD && XP_WIN && _M_X64
+
 static nsCString CurrentRemoteType() {
   MOZ_ASSERT(XRE_IsParentProcess() || XRE_IsContentProcess());
   if (ContentChild* cc = ContentChild::GetSingleton()) {
@@ -773,6 +791,11 @@ LoadInfo::LoadInfo(
       mHasInjectedCookieForCookieBannerHandling(
           aHasInjectedCookieForCookieBannerHandling),
       mWasSchemelessInput(aWasSchemelessInput) {
+#if defined(NIGHTLY_BUILD) && defined(XP_WIN) && defined(_M_X64)
+  if (mReservedClientInfo.isSome()) {
+    mReservedClientInfoEmplaceTrace.Fill();
+  }
+#endif  // NIGHTLY_BUILD && XP_WIN && _M_X64
   // Only top level TYPE_DOCUMENT loads can have a null loadingPrincipal
   MOZ_ASSERT(mLoadingPrincipal ||
              aContentPolicyType == nsIContentPolicy::TYPE_DOCUMENT);
@@ -2126,6 +2149,15 @@ UniquePtr<ClientSource> LoadInfo::TakeReservedClientSource() {
   return std::move(mReservedClientSource);
 }
 
+#if defined(NIGHTLY_BUILD) && defined(XP_WIN) && defined(_M_X64)
+[[clang::optnone]] MOZ_NEVER_INLINE static void CrashWithEmplaceTrace(
+    const LoadInfo::StackTrace& aEmplaceStackTrace) {
+  // Make a copy of the stack trace available on the crashing thread's stack
+  LoadInfo::StackTrace emplaceStackTrace [[maybe_unused]]{aEmplaceStackTrace};
+  MOZ_CRASH("mReservedClientInfo already set, emplace stack trace available");
+}
+#endif  // NIGHTLY_BUILD && XP_WIN && _M_X64
+
 void LoadInfo::SetReservedClientInfo(const ClientInfo& aClientInfo) {
   MOZ_DIAGNOSTIC_ASSERT(mInitialClientInfo.isNothing());
   // Treat assignments of the same value as a no-op.  The emplace below
@@ -2134,10 +2166,16 @@ void LoadInfo::SetReservedClientInfo(const ClientInfo& aClientInfo) {
     if (mReservedClientInfo.ref() == aClientInfo) {
       return;
     }
+#if defined(NIGHTLY_BUILD) && defined(XP_WIN) && defined(_M_X64)
+    CrashWithEmplaceTrace(mReservedClientInfoEmplaceTrace);
+#endif  // NIGHTLY_BUILD && XP_WIN && _M_X64
     MOZ_DIAGNOSTIC_ASSERT(false, "mReservedClientInfo already set");
     mReservedClientInfo.reset();
   }
   mReservedClientInfo.emplace(aClientInfo);
+#if defined(NIGHTLY_BUILD) && defined(XP_WIN) && defined(_M_X64)
+  mReservedClientInfoEmplaceTrace.Fill();
+#endif  // NIGHTLY_BUILD && XP_WIN && _M_X64
 }
 
 void LoadInfo::OverrideReservedClientInfoInParent(
@@ -2148,6 +2186,9 @@ void LoadInfo::OverrideReservedClientInfoInParent(
   mInitialClientInfo.reset();
   mReservedClientInfo.reset();
   mReservedClientInfo.emplace(aClientInfo);
+#if defined(NIGHTLY_BUILD) && defined(XP_WIN) && defined(_M_X64)
+  mReservedClientInfoEmplaceTrace.Fill();
+#endif  // NIGHTLY_BUILD && XP_WIN && _M_X64
 }
 
 const Maybe<ClientInfo>& LoadInfo::GetReservedClientInfo() {

netwerk/base/LoadInfo.h

@@ -305,6 +305,32 @@ class LoadInfo final : public nsILoadInfo {
   Maybe<mozilla::dom::ClientInfo> mClientInfo;
   UniquePtr<mozilla::dom::ClientSource> mReservedClientSource;
   Maybe<mozilla::dom::ClientInfo> mReservedClientInfo;
+
+// Diagnostics code for bug 1761208
+#if defined(NIGHTLY_BUILD) && defined(XP_WIN) && defined(_M_X64)
+ public:
+  class StackTrace {
+   public:
+    static const size_t kMaxFrames = 24;
+
+    // The number of PCs in the stack trace.
+    size_t mLength;
+
+    // The PCs in the stack trace. Only the first mLength are initialized.
+    const void* mPcs[kMaxFrames];
+
+   public:
+    void Fill();
+
+   private:
+    static void StackWalkCallback(uint32_t aFrameNumber, void* aPc, void* aSp,
+                                  void* aClosure);
+  };
+
+ private:
+  StackTrace mReservedClientInfoEmplaceTrace;
+#endif  // NIGHTLY_BUILD && XP_WIN && _M_X64
+
   Maybe<mozilla::dom::ClientInfo> mInitialClientInfo;
   Maybe<mozilla::dom::ServiceWorkerDescriptor> mController;
   RefPtr<mozilla::dom::PerformanceStorage> mPerformanceStorage;