Index: include/sanitizer/dfsan_interface.h
===================================================================
--- include/sanitizer/dfsan_interface.h
+++ include/sanitizer/dfsan_interface.h
@@ -52,6 +52,9 @@
 /// Sets the label for each address in [addr,addr+size) to \c label.
 void dfsan_set_label(dfsan_label label, void *addr, size_t size);
 
+/// In process reset of dfsan
+void dfsan_reset(void);
+
 /// Sets the label for each address in [addr,addr+size) to the union of the
 /// current label for that address and \c label.
 void dfsan_add_label(dfsan_label label, void *addr, size_t size);
Index: lib/dfsan/dfsan.h
===================================================================
--- lib/dfsan/dfsan.h
+++ lib/dfsan/dfsan.h
@@ -34,6 +34,7 @@
 extern "C" {
 void dfsan_add_label(dfsan_label label, void *addr, uptr size);
 void dfsan_set_label(dfsan_label label, void *addr, uptr size);
+void dfsan_reset(void);
 dfsan_label dfsan_read_label(const void *addr, uptr size);
 dfsan_label dfsan_union(dfsan_label l1, dfsan_label l2);
 }  // extern "C"
Index: lib/dfsan/dfsan.cc
===================================================================
--- lib/dfsan/dfsan.cc
+++ lib/dfsan/dfsan.cc
@@ -158,6 +158,27 @@
   }
 }
 
+// Reset labels and shadow memory for dfsan to restart from clean.
+extern "C" SANITIZER_INTERFACE_ATTRIBUTE
+void dfsan_reset(void) {
+  // reset shadow memory
+  MmapFixedNoReserve(ShadowAddr(), UnusedAddr() - ShadowAddr());
+
+  dfsan_label last_label =
+      atomic_load(&__dfsan_last_label, memory_order_relaxed);
+
+  // reset potentially polluted union table entries
+  for (uptr l = 0; l <= last_label; ++l) {
+    for (uptr m = 0; m <= last_label; ++m) {
+      atomic_dfsan_label *table_ent = union_table(l, m);
+      dfsan_label label = 0;
+      atomic_store(table_ent, label, memory_order_acquire);
+    }
+  }
+  // reset label count
+  atomic_store(&__dfsan_last_label, 0, memory_order_relaxed);
+}
+
 // Resolves the union of two unequal labels.  Nonequality is a precondition for
 // this function (the instrumentation pass inlines the equality test).
 extern "C" SANITIZER_INTERFACE_ATTRIBUTE
Index: lib/dfsan/done_abilist.txt
===================================================================
--- lib/dfsan/done_abilist.txt
+++ lib/dfsan/done_abilist.txt
@@ -6,6 +6,8 @@
 ###############################################################################
 fun:dfsan_union=uninstrumented
 fun:dfsan_union=discard
+fun:dfsan_reset=uninstrumented
+fun:dfsan_reset=discard
 fun:dfsan_create_label=uninstrumented
 fun:dfsan_create_label=discard
 fun:dfsan_set_label=uninstrumented
Index: test/dfsan/reset.cc
===================================================================
--- /dev/null
+++ test/dfsan/reset.cc
@@ -0,0 +1,22 @@
+// RUN: %clang_dfsan %s -o %t && %run %t
+// RUN: %clang_dfsan -mllvm -dfsan-args-abi %s -o %t && %run %t
+
+// Tests that dfsan runtime is reset correctly.
+
+#include <sanitizer/dfsan_interface.h>
+#include <assert.h>
+
+int main(void) {
+  int i = 1;
+  int j = 1;
+  dfsan_label i_label = dfsan_create_label("i", 0);
+  dfsan_set_label(i_label, &i, sizeof(i));
+  dfsan_label j_label = dfsan_create_label("j", 0);
+  dfsan_add_label(j_label, &j, sizeof(j));
+  assert(dfsan_get_label_count() == 2);
+
+  dfsan_reset();
+  assert(dfsan_get_label_count() == 0);
+
+  return 0;
+}