Fix a race reading 'warmingUp' to decide request kind

Summary:There was a race reading the global 'warmingUp' flag which could potentially
cause a request to start JITing (and thus marking hot functions and freeing
s_func_counters) while later requests were still profiling (and thus writting to
s_func_counters).  This diff fixes the issue by reading the 'warmingUp' just
once per request to decide its kind.

Reviewed By: swtaarrs

Differential Revision: D3051381

fb-gh-sync-id: e1f2327526064aa9237d528e5dcc8fa787c24981
shipit-source-id: e1f2327526064aa9237d528e5dcc8fa787c24981

hphp/runtime/vm/type-profile.cpp

@@ -54,7 +54,8 @@ void profileInit() {
  * In server mode, we exclude warmup document requests from profiling, then
  * record samples for EvalJitProfileInterpRequests standard requests.
  */
-bool __thread profileOn = false;
+
+RequestKind __thread requestKind = RequestKind::Warmup;
 static bool warmingUp;
 static int64_t numRequests;
 bool __thread standardRequest = true;
@@ -161,17 +162,18 @@ static inline bool doneProfiling() {
      !RuntimeOption::EvalJitProfileRecord);
 }
 
-static inline bool profileThisRequest() {
-  if (warmingUp) return false;
-  if (doneProfiling()) return false;
-  if (RuntimeOption::ServerExecutionMode()) return true;
-  return RuntimeOption::EvalJitProfileRecord;
+static inline RequestKind getRequestKind() {
+  if (warmingUp) return RequestKind::Warmup;
+  if (doneProfiling()) return RequestKind::Standard;
+  if (RuntimeOption::ServerExecutionMode() ||
+      RuntimeOption::EvalJitProfileRecord) return RequestKind::Profile;
+  return RequestKind::Standard;
 }
 
 void profileRequestStart() {
-  profileOn = profileThisRequest();
+  requestKind = getRequestKind();
 
-  bool okToJit = !warmingUp && !profileOn;
+  bool okToJit = requestKind == RequestKind::Standard;
   if (okToJit) {
     jit::Lease::mayLock(true);
     if (singleJitRequests < RuntimeOption::EvalNumSingleJitRequests) {

hphp/runtime/vm/type-profile.h

@@ -26,6 +26,12 @@ namespace HPHP {
 
 struct Func;
 
+enum class RequestKind {
+  Warmup,
+  Profile,
+  Standard
+};
+
 //////////////////////////////////////////////////////////////////////
 
 void profileInit();
@@ -43,9 +49,9 @@ int64_t requestCount();
  */
 void profileIncrementFuncCounter(const Func*);
 
-extern __thread bool profileOn;
+extern __thread RequestKind requestKind;
 inline bool isProfileRequest() {
-  return profileOn;
+  return requestKind == RequestKind::Profile;
 }
 
 extern __thread bool standardRequest;