core: Clear ConfigSelector in panic mode

core/src/main/java/io/grpc/internal/ManagedChannelImpl.java

@@ -887,6 +887,7 @@ public String toString() {
     }
 
     updateSubchannelPicker(new PanicSubchannelPicker());
+    realChannel.updateConfigSelector(null);
     channelLogger.log(ChannelLogLevel.ERROR, "PANIC! Entering TRANSIENT_FAILURE");
     channelStateManager.gotoState(TRANSIENT_FAILURE);
   }
@@ -1755,6 +1756,9 @@ final class NamesResolved implements Runnable {
         @SuppressWarnings("ReferenceEquality")
         @Override
         public void run() {
+          if (ManagedChannelImpl.this.nameResolver != resolver) {
+            return;
+          }
 
           List<EquivalentAddressGroup> servers = resolutionResult.getAddresses();
           channelLogger.log(

core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java

@@ -2799,6 +2799,40 @@ public void run() {
     panicExpected = true;
   }
 
+  @Test
+  public void panic_atStart() {
+    final RuntimeException panicReason = new RuntimeException("Simulated NR exception");
+    final NameResolver failingResolver = new NameResolver() {
+      @Override public String getServiceAuthority() {
+        return "fake-authority";
+      }
+
+      @Override public void start(Listener2 listener) {
+        throw panicReason;
+      }
+
+      @Override public void shutdown() {}
+    };
+    channelBuilder.nameResolverFactory(new NameResolver.Factory() {
+      @Override public NameResolver newNameResolver(URI targetUri, NameResolver.Args args) {
+        return failingResolver;
+      }
+
+      @Override public String getDefaultScheme() {
+        return "fakescheme";
+      }
+    });
+    createChannel();
+
+    // RPCs fail immediately
+    ClientCall<String, Integer> call =
+        channel.newCall(method, CallOptions.DEFAULT.withoutWaitForReady());
+    call.start(mockCallListener, new Metadata());
+    executor.runDueTasks();
+    verifyCallListenerClosed(mockCallListener, Status.Code.INTERNAL, panicReason);
+    panicExpected = true;
+  }
+
   private void verifyPanicMode(Throwable cause) {
     panicExpected = true;
     @SuppressWarnings("unchecked")