diff --git a/lldb/include/lldb/Breakpoint/Breakpoint.h b/lldb/include/lldb/Breakpoint/Breakpoint.h
--- a/lldb/include/lldb/Breakpoint/Breakpoint.h
+++ b/lldb/include/lldb/Breakpoint/Breakpoint.h
@@ -382,7 +382,10 @@
   /// \param[in] is_synchronous
   ///    If \b true the callback will be run on the private event thread
   ///    before the stop event gets reported.  If false, the callback will get
-  ///    handled on the public event thread after the stop has been posted.
+  ///    handled on the public event thread while the stop event is being
+  ///    pulled off the event queue.
+  ///    Note: synchronous callbacks cannot cause the target to run, in
+  ///    particular, they should not try to run the expression evaluator.
   void SetCallback(BreakpointHitCallback callback, void *baton,
                    bool is_synchronous = false);
 
diff --git a/lldb/source/Plugins/InstrumentationRuntime/ASan/InstrumentationRuntimeASan.cpp b/lldb/source/Plugins/InstrumentationRuntime/ASan/InstrumentationRuntimeASan.cpp
--- a/lldb/source/Plugins/InstrumentationRuntime/ASan/InstrumentationRuntimeASan.cpp
+++ b/lldb/source/Plugins/InstrumentationRuntime/ASan/InstrumentationRuntimeASan.cpp
@@ -306,7 +306,7 @@
           .CreateBreakpoint(symbol_address, internal, hardware)
           .get();
   breakpoint->SetCallback(InstrumentationRuntimeASan::NotifyBreakpointHit, this,
-                          true);
+                          false);
   breakpoint->SetBreakpointKind("address-sanitizer-report");
   SetBreakpointID(breakpoint->GetID());
 
diff --git a/lldb/source/Plugins/InstrumentationRuntime/MainThreadChecker/InstrumentationRuntimeMainThreadChecker.cpp b/lldb/source/Plugins/InstrumentationRuntime/MainThreadChecker/InstrumentationRuntimeMainThreadChecker.cpp
--- a/lldb/source/Plugins/InstrumentationRuntime/MainThreadChecker/InstrumentationRuntimeMainThreadChecker.cpp
+++ b/lldb/source/Plugins/InstrumentationRuntime/MainThreadChecker/InstrumentationRuntimeMainThreadChecker.cpp
@@ -215,7 +215,7 @@
                             /*hardware=*/false)
           .get();
   breakpoint->SetCallback(
-      InstrumentationRuntimeMainThreadChecker::NotifyBreakpointHit, this, true);
+      InstrumentationRuntimeMainThreadChecker::NotifyBreakpointHit, this, false);
   breakpoint->SetBreakpointKind("main-thread-checker-report");
   SetBreakpointID(breakpoint->GetID());
 
diff --git a/lldb/source/Plugins/InstrumentationRuntime/TSan/InstrumentationRuntimeTSan.cpp b/lldb/source/Plugins/InstrumentationRuntime/TSan/InstrumentationRuntimeTSan.cpp
--- a/lldb/source/Plugins/InstrumentationRuntime/TSan/InstrumentationRuntimeTSan.cpp
+++ b/lldb/source/Plugins/InstrumentationRuntime/TSan/InstrumentationRuntimeTSan.cpp
@@ -922,7 +922,7 @@
           .CreateBreakpoint(symbol_address, internal, hardware)
           .get();
   breakpoint->SetCallback(InstrumentationRuntimeTSan::NotifyBreakpointHit, this,
-                          true);
+                          false);
   breakpoint->SetBreakpointKind("thread-sanitizer-report");
   SetBreakpointID(breakpoint->GetID());
 
diff --git a/lldb/source/Plugins/InstrumentationRuntime/UBSan/InstrumentationRuntimeUBSan.cpp b/lldb/source/Plugins/InstrumentationRuntime/UBSan/InstrumentationRuntimeUBSan.cpp
--- a/lldb/source/Plugins/InstrumentationRuntime/UBSan/InstrumentationRuntimeUBSan.cpp
+++ b/lldb/source/Plugins/InstrumentationRuntime/UBSan/InstrumentationRuntimeUBSan.cpp
@@ -276,7 +276,7 @@
                             /*hardware=*/false)
           .get();
   breakpoint->SetCallback(InstrumentationRuntimeUBSan::NotifyBreakpointHit,
-                          this, true);
+                          this, false);
   breakpoint->SetBreakpointKind("undefined-behavior-sanitizer-report");
   SetBreakpointID(breakpoint->GetID());
 
diff --git a/lldb/test/API/functionalities/ubsan/basic/TestUbsanBasic.py b/lldb/test/API/functionalities/ubsan/basic/TestUbsanBasic.py
--- a/lldb/test/API/functionalities/ubsan/basic/TestUbsanBasic.py
+++ b/lldb/test/API/functionalities/ubsan/basic/TestUbsanBasic.py
@@ -86,4 +86,9 @@
         self.assertEqual(os.path.basename(data["filename"]), "main.c")
         self.assertEqual(data["line"], self.line_align)
 
-        self.runCmd("continue")
+        for count in range(0,8):
+            process.Continue()
+            stop_reason = thread.GetStopReason()
+            self.assertEqual(stop_reason, lldb.eStopReasonInstrumentation,
+                             "Round {0} wasn't instrumentation".format(count))
+
diff --git a/lldb/test/API/functionalities/ubsan/basic/main.c b/lldb/test/API/functionalities/ubsan/basic/main.c
--- a/lldb/test/API/functionalities/ubsan/basic/main.c
+++ b/lldb/test/API/functionalities/ubsan/basic/main.c
@@ -1,4 +1,16 @@
 int main() {
   int data[4];
-  return *(int *)(((char *)&data[0]) + 2); // align line
+  int result = *(int *)(((char *)&data[0]) + 2); // align line
+
+  int *p = data + 5;  // Index 5 out of bounds for type 'int [4]'
+  *p = data + 5;
+  *p = data + 5;
+  *p = data + 5;
+  *p = data + 5;
+  *p = data + 5;
+  *p = data + 5;
+  *p = data + 5;
+  *p = data + 5;
+
+  return 0;
 }