diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -1143,6 +1143,7 @@
   // runtime's functionality.
   if (hasExportSymbolDirective(Args)) {
     if (ForGCOV) {
+      addExportedSymbol(CmdArgs, "___gcov_fork");
       addExportedSymbol(CmdArgs, "___gcov_flush");
       addExportedSymbol(CmdArgs, "_flush_fn_list");
       addExportedSymbol(CmdArgs, "_writeout_fn_list");
diff --git a/compiler-rt/lib/profile/GCDAProfiling.c b/compiler-rt/lib/profile/GCDAProfiling.c
--- a/compiler-rt/lib/profile/GCDAProfiling.c
+++ b/compiler-rt/lib/profile/GCDAProfiling.c
@@ -71,6 +71,9 @@
 static __inline void gcov_flush_unlock() {
   pthread_mutex_unlock(&gcov_flush_mutex);
 }
+static __inline void gcov_flush_init_mutex() {
+  pthread_mutex_init(&gcov_flush_mutex, NULL);
+}
 #else
 #include <windows.h>
 static SRWLOCK gcov_flush_mutex = SRWLOCK_INIT;
@@ -80,6 +83,9 @@
 static __inline void gcov_flush_unlock() {
   ReleaseSRWLockExclusive(&gcov_flush_mutex);
 }
+static __inline void gcov_flush_init_mutex() {
+  InitializeSRWLock(&gcov_flush_mutex);
+}
 #endif
 
 /* #define DEBUG_GCDAPROFILING */
@@ -638,6 +644,16 @@
   fn_list_insert(&flush_fn_list, fn);
 }
 
+pid_t __gcov_fork() {
+  pid_t pid = fork();
+
+  if (pid == 0) {
+    gcov_flush_init_mutex();
+  }
+
+  return pid;
+}
+
 void __gcov_flush() {
   gcov_flush_lock();
 
diff --git a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
--- a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
@@ -631,20 +631,22 @@
 }
 
 void GCOVProfiler::AddFlushBeforeForkAndExec() {
-  SmallVector<Instruction *, 2> ForkAndExecs;
+  SmallVector<std::pair<bool, CallInst *>, 2> ForksAndExecs;
   for (auto &F : M->functions()) {
     auto *TLI = &GetTLI(F);
     for (auto &I : instructions(F)) {
       if (CallInst *CI = dyn_cast<CallInst>(&I)) {
         if (Function *Callee = CI->getCalledFunction()) {
           LibFunc LF;
-          if (TLI->getLibFunc(*Callee, LF) &&
-              (LF == LibFunc_fork || LF == LibFunc_execl ||
-               LF == LibFunc_execle || LF == LibFunc_execlp ||
-               LF == LibFunc_execv || LF == LibFunc_execvp ||
-               LF == LibFunc_execve || LF == LibFunc_execvpe ||
-               LF == LibFunc_execvP)) {
-            ForkAndExecs.push_back(&I);
+          if (TLI->getLibFunc(*Callee, LF)) {
+            if (LF == LibFunc_fork) {
+              ForksAndExecs.push_back({true, CI});
+            } else if (LF == LibFunc_execl || LF == LibFunc_execle ||
+                       LF == LibFunc_execlp || LF == LibFunc_execv ||
+                       LF == LibFunc_execvp || LF == LibFunc_execve ||
+                       LF == LibFunc_execvpe || LF == LibFunc_execvP) {
+              ForksAndExecs.push_back({false, CI});
+            }
           }
         }
       }
@@ -654,12 +656,21 @@
   // We need to split the block after the fork/exec call
   // because else the counters for the lines after will be
   // the same as before the call.
-  for (auto I : ForkAndExecs) {
-    IRBuilder<> Builder(I);
+  for (auto F : ForksAndExecs) {
+    IRBuilder<> Builder(F.second);
     FunctionType *FTy = FunctionType::get(Builder.getVoidTy(), {}, false);
     FunctionCallee GCOVFlush = M->getOrInsertFunction("__gcov_flush", FTy);
     Builder.CreateCall(GCOVFlush);
-    I->getParent()->splitBasicBlock(I);
+
+    if (F.first) {
+      // We've a fork, so we call a custom fork which will initialize the mutex
+      // used when flushing
+      FTy = FunctionType::get(Builder.getInt32Ty(), {}, false);
+      FunctionCallee GCOVFork = M->getOrInsertFunction("__gcov_fork", FTy);
+      F.second->setCalledFunction(GCOVFork);
+    }
+
+    F.second->getParent()->splitBasicBlock(F.second);
   }
 }