Fix TSAN reported failure

src/core/channel/client_channel.c

@@ -236,18 +236,15 @@ static void picked_target(void *arg, int iomgr_success) {
   }
 }
 
-static void pick_target(grpc_lb_policy *lb_policy, call_data *calld) {
+static void pick_target(
+    grpc_lb_policy *lb_policy, call_data *calld, grpc_pollset *bind_pollset) {
   grpc_metadata_batch *initial_metadata;
   grpc_transport_stream_op *op = &calld->waiting_op;
 
-  GPR_ASSERT(op->bind_pollset);
-  GPR_ASSERT(op->send_ops);
-  GPR_ASSERT(op->send_ops->nops >= 1);
-  GPR_ASSERT(op->send_ops->ops[0].type == GRPC_OP_METADATA);
   initial_metadata = &op->send_ops->ops[0].data.metadata;
 
   grpc_iomgr_closure_init(&calld->async_setup_task, picked_target, calld);
-  grpc_lb_policy_pick(lb_policy, op->bind_pollset, initial_metadata,
+  grpc_lb_policy_pick(lb_policy, bind_pollset, initial_metadata,
                       &calld->picked_channel, &calld->async_setup_task);
 }
 
@@ -358,12 +355,19 @@ static void perform_transport_stream_op(grpc_call_element *elem,
           gpr_mu_lock(&chand->mu_config);
           lb_policy = chand->lb_policy;
           if (lb_policy) {
+            grpc_pollset *bind_pollset = calld->waiting_op.bind_pollset;
             GRPC_LB_POLICY_REF(lb_policy, "pick");
             gpr_mu_unlock(&chand->mu_config);
             calld->state = CALL_WAITING_FOR_PICK;
+
+            GPR_ASSERT(calld->waiting_op.bind_pollset);
+            GPR_ASSERT(calld->waiting_op.send_ops);
+            GPR_ASSERT(calld->waiting_op.send_ops->nops >= 1);
+            GPR_ASSERT(
+                calld->waiting_op.send_ops->ops[0].type == GRPC_OP_METADATA);
             gpr_mu_unlock(&calld->mu_state);
 
-            pick_target(lb_policy, calld);
+            pick_target(lb_policy, calld, bind_pollset);
 
             GRPC_LB_POLICY_UNREF(lb_policy, "pick");
           } else if (chand->resolver != NULL) {