Merge pull request #23073 from markdroth/xds_subchannel_sharing_fix

Remove XdsClient from channel args to fix subchannel sharing.

src/core/ext/filters/client_channel/lb_policy/xds/eds.cc

@@ -32,6 +32,7 @@
 #include "src/core/ext/filters/client_channel/lb_policy_factory.h"
 #include "src/core/ext/filters/client_channel/lb_policy_registry.h"
 #include "src/core/ext/filters/client_channel/server_address.h"
+#include "src/core/ext/filters/client_channel/xds/xds_channel_args.h"
 #include "src/core/ext/filters/client_channel/xds/xds_client.h"
 #include "src/core/ext/filters/client_channel/xds/xds_client_stats.h"
 #include "src/core/lib/channel/channel_args.h"
@@ -715,11 +716,18 @@ grpc_channel_args* EdsLb::CreateChildPolicyArgsLocked(
       grpc_channel_arg_integer_create(
           const_cast<char*>(GRPC_ARG_INHIBIT_HEALTH_CHECKING), 1),
   };
+  absl::InlinedVector<const char*, 1> args_to_remove;
   if (xds_client_from_channel_ == nullptr) {
     args_to_add.emplace_back(xds_client_->MakeChannelArg());
-  }
-  return grpc_channel_args_copy_and_add(args, args_to_add.data(),
-                                        args_to_add.size());
+  } else if (!config_->lrs_load_reporting_server_name().has_value()) {
+    // Remove XdsClient from channel args, so that its presence doesn't
+    // prevent us from sharing subchannels between channels.
+    // If load reporting is enabled, this happens in the LRS policy instead.
+    args_to_remove.push_back(GRPC_ARG_XDS_CLIENT);
+  }
+  return grpc_channel_args_copy_and_add_and_remove(
+      args, args_to_remove.data(), args_to_remove.size(), args_to_add.data(),
+      args_to_add.size());
 }
 
 OrphanablePtr<LoadBalancingPolicy> EdsLb::CreateChildPolicyLocked(

src/core/ext/filters/client_channel/lb_policy/xds/lrs.cc

@@ -254,9 +254,11 @@ void LrsLb::UpdateLocked(UpdateArgs args) {
         config_->eds_service_name(), config_->locality_name());
     MaybeUpdatePickerLocked();
   }
+  // Remove XdsClient from channel args, so that its presence doesn't
+  // prevent us from sharing subchannels between channels.
+  grpc_channel_args* new_args = XdsClient::RemoveFromChannelArgs(*args.args);
   // Update child policy.
-  UpdateChildPolicyLocked(std::move(args.addresses), args.args);
-  args.args = nullptr;  // Ownership passed to UpdateChildPolicyLocked().
+  UpdateChildPolicyLocked(std::move(args.addresses), new_args);
 }
 
 void LrsLb::MaybeUpdatePickerLocked() {

src/core/ext/filters/client_channel/xds/xds_client.cc

@@ -2387,4 +2387,10 @@ RefCountedPtr<XdsClient> XdsClient::GetFromChannelArgs(
   return nullptr;
 }
 
+grpc_channel_args* XdsClient::RemoveFromChannelArgs(
+    const grpc_channel_args& args) {
+  const char* arg_name = GRPC_ARG_XDS_CLIENT;
+  return grpc_channel_args_copy_and_remove(&args, &arg_name, 1);
+}
+
 }  // namespace grpc_core

src/core/ext/filters/client_channel/xds/xds_client.h

@@ -142,6 +142,8 @@ class XdsClient : public InternallyRefCounted<XdsClient> {
   grpc_arg MakeChannelArg() const;
   static RefCountedPtr<XdsClient> GetFromChannelArgs(
       const grpc_channel_args& args);
+  static grpc_channel_args* RemoveFromChannelArgs(
+      const grpc_channel_args& args);
 
  private:
   // Contains a channel to the xds server and all the data related to the