In ProfilerSignalHandler ensure that thread we are trying to sample locked the isolate.

src/platform-freebsd.cc

Index: src/platform-freebsd.cc
diff --git a/src/platform-freebsd.cc b/src/platform-freebsd.cc
index ca4e54f6fca5501951d949f9019f2f275cfdf6ba..8b83f2bd6cb1c85a34e4a3476bbe8366194b6f94 100644
--- a/src/platform-freebsd.cc
+++ b/src/platform-freebsd.cc
@@ -642,6 +642,11 @@ static void ProfilerSignalHandler(int signal, siginfo_t* info, void* context) {
     // We require a fully initialized and entered isolate.
     return;
   }
+  if (v8::Locker::IsActive() &&
+      !isolate->thread_manager()->IsLockedByCurrentThread()) {
+    return;
+  }
+
   Sampler* sampler = isolate->logger()->sampler();
   if (sampler == NULL || !sampler->IsActive()) return;