From cbfd8e4405e2892f414ce01e612d688c33a58715 Mon Sep 17 00:00:00 2001
From: Philippe Canal <pcanal@fnal.gov>
Date: Mon, 25 Jan 2021 13:44:57 -0600
Subject: [PATCH] Fix #7093: race condition tripping TEnum::GetEnum

---
 core/meta/src/TEnum.cxx       | 8 +++++---
 core/metacling/src/TCling.cxx | 5 ++++-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/core/meta/src/TEnum.cxx b/core/meta/src/TEnum.cxx
index 25a588e931c61..a3798271faebb 100644
--- a/core/meta/src/TEnum.cxx
+++ b/core/meta/src/TEnum.cxx
@@ -195,9 +195,7 @@ TEnum *TEnum::GetEnum(const char *enumName, ESearchAction sa)
          return en;
       }
 
-      // Lock need for gROOT->GetListOfClasses() and the later update/modification to
-      // the autoparsing state.
-      R__LOCKGUARD(gInterpreterMutex);
+
       if (auto tClassScope = static_cast<TClass *>(gROOT->GetListOfClasses()->FindObject(scopeName))) {
          // If this is a class, load only if the user allowed interpreter lookup
          // If this is a namespace and the user did not allow for interpreter lookup, load but before disable
@@ -236,6 +234,10 @@ TEnum *TEnum::GetEnum(const char *enumName, ESearchAction sa)
       return nullptr;
    }
 
+   // Keep the state consistent.  I particular prevent change in the state of AutoLoading and AutoParsing allowance
+   // and gROOT->GetListOfClasses() and the later update/modification to the autoparsing state.
+   R__READ_LOCKGUARD(ROOT::gCoreMutex);
+
    if (lastPos != enumName) {
       // We have a scope
       // All of this C gymnastic is to avoid allocations on the heap (see TClingLookupHelper__ExistingTypeCheck)
diff --git a/core/metacling/src/TCling.cxx b/core/metacling/src/TCling.cxx
index a5a60e681e375..c7fd3c78707da 100644
--- a/core/metacling/src/TCling.cxx
+++ b/core/metacling/src/TCling.cxx
@@ -6028,6 +6028,9 @@ Int_t TCling::DeepAutoLoadImpl(const char *cls)
 
 Int_t TCling::AutoLoad(const char *cls, Bool_t knowDictNotLoaded /* = kFALSE */)
 {
+   // Prevent update to IsClassAutoloading between our check and our actions.
+   R__READ_LOCKGUARD(ROOT::gCoreMutex);
+
    // TClass::GetClass explicitly calls gInterpreter->AutoLoad. When called from
    // rootcling (in *_rdict.pcm file generation) it is a no op.
    // FIXME: We should avoid calling autoload when we know we are not supposed
@@ -6042,7 +6045,7 @@ Int_t TCling::AutoLoad(const char *cls, Bool_t knowDictNotLoaded /* = kFALSE */)
 
    assert(IsClassAutoLoadingEnabled() && "Calling when AutoLoading is off!");
 
-   R__LOCKGUARD(gInterpreterMutex);
+   R__WRITE_LOCKGUARD(ROOT::gCoreMutex);
 
    if (!knowDictNotLoaded && gClassTable->GetDictNorm(cls)) {
       // The library is already loaded as the class's dictionary is known.