[release/6.0] Fix frequent FuncEval abort upon hitting a breakpoint in an ASP.NET Core web app

src/coreclr/vm/appdomain.cpp

@@ -3709,7 +3709,9 @@ BOOL AppDomain::AddFileToCache(AssemblySpec* pSpec, PEAssembly *pFile, BOOL fAll
     }
     CONTRACTL_END;
 
-    CrstHolder holder(&m_DomainCacheCrst);
+    GCX_PREEMP();
+    DomainCacheCrstHolderForGCCoop holder(this);
+
     // !!! suppress exceptions
     if(!m_AssemblyCache.StoreFile(pSpec, pFile) && !fAllowFailure)
     {
@@ -3739,7 +3741,9 @@ BOOL AppDomain::AddAssemblyToCache(AssemblySpec* pSpec, DomainAssembly *pAssembl
     }
     CONTRACTL_END;
 
-    CrstHolder holder(&m_DomainCacheCrst);
+    GCX_PREEMP();
+    DomainCacheCrstHolderForGCCoop holder(this);
+
     // !!! suppress exceptions
     BOOL bRetVal = m_AssemblyCache.StoreAssembly(pSpec, pAssembly);
     return bRetVal;
@@ -3760,7 +3764,9 @@ BOOL AppDomain::AddExceptionToCache(AssemblySpec* pSpec, Exception *ex)
     if (ex->IsTransient())
         return TRUE;
 
-    CrstHolder holder(&m_DomainCacheCrst);
+    GCX_PREEMP();
+    DomainCacheCrstHolderForGCCoop holder(this);
+
     // !!! suppress exceptions
     return m_AssemblyCache.StoreException(pSpec, ex);
 }
@@ -3778,7 +3784,7 @@ void AppDomain::AddUnmanagedImageToCache(LPCWSTR libraryName, NATIVE_LIBRARY_HAN
     }
     CONTRACTL_END;
 
-    CrstHolder lock(&m_DomainCacheCrst);
+    DomainCacheCrstHolderForGCPreemp lock(this);
 
     const UnmanagedImageCacheEntry *existingEntry = m_unmanagedCache.LookupPtr(libraryName);
     if (existingEntry != NULL)
@@ -3808,7 +3814,8 @@ NATIVE_LIBRARY_HANDLE AppDomain::FindUnmanagedImageInCache(LPCWSTR libraryName)
     }
     CONTRACT_END;
 
-    CrstHolder lock(&m_DomainCacheCrst);
+    DomainCacheCrstHolderForGCPreemp lock(this);
+
     const UnmanagedImageCacheEntry *existingEntry = m_unmanagedCache.LookupPtr(libraryName);
     if (existingEntry == NULL)
         RETURN NULL;
@@ -3850,7 +3857,8 @@ BOOL AppDomain::RemoveAssemblyFromCache(DomainAssembly* pAssembly)
     }
     CONTRACTL_END;
 
-    CrstHolder holder(&m_DomainCacheCrst);
+    GCX_PREEMP();
+    DomainCacheCrstHolderForGCCoop holder(this);
 
     return m_AssemblyCache.RemoveAssembly(pAssembly);
 }

src/coreclr/vm/appdomain.hpp

@@ -1171,6 +1171,30 @@ class BaseDomain
     };
     friend class LockHolder;
 
+    // To be used when the thread will remain in preemptive GC mode while holding the lock
+    class DomainCacheCrstHolderForGCPreemp : private CrstHolder
+    {
+    public:
+        DomainCacheCrstHolderForGCPreemp(BaseDomain *pD)
+            : CrstHolder(&pD->m_DomainCacheCrst)
+        {
+            WRAPPER_NO_CONTRACT;
+        }
+    };
+
+    // To be used when the thread may enter cooperative GC mode while holding the lock. The thread enters a
+    // forbid-suspend-for-debugger region along with acquiring the lock, such that it would not suspend for the debugger while
+    // holding the lock, as that may otherwise cause a FuncEval to deadlock when trying to acquire the lock.
+    class DomainCacheCrstHolderForGCCoop : private CrstAndForbidSuspendForDebuggerHolder
+    {
+    public:
+        DomainCacheCrstHolderForGCCoop(BaseDomain *pD)
+            : CrstAndForbidSuspendForDebuggerHolder(&pD->m_DomainCacheCrst)
+        {
+            WRAPPER_NO_CONTRACT;
+        }
+    };
+
     class DomainLocalBlockLockHolder : public CrstHolder
     {
     public:

src/coreclr/vm/crst.cpp

@@ -789,8 +789,8 @@ CrstBase::CrstAndForbidSuspendForDebuggerHolder::CrstAndForbidSuspendForDebugger
     // Reentrant locks are currently not supported
     _ASSERTE((pCrst->m_dwFlags & CRST_REENTRANCY) == 0);
 
-    Thread *pThread = GetThread();
-    if (pThread->IsInForbidSuspendForDebuggerRegion())
+    Thread *pThread = GetThreadNULLOk();
+    if (pThread == nullptr || pThread->IsInForbidSuspendForDebuggerRegion())
     {
         AcquireLock(pCrst);
         return;