diff --git a/src/core/ext/client_channel/client_channel.c b/src/core/ext/client_channel/client_channel.c
index b1a4aa9a1ca..6cbc333b832 100644
--- a/src/core/ext/client_channel/client_channel.c
+++ b/src/core/ext/client_channel/client_channel.c
@@ -230,7 +230,7 @@ static void on_lb_policy_state_changed_locked(grpc_exec_ctx *exec_ctx,
   if (w->lb_policy == w->chand->lb_policy) {
     if (publish_state == GRPC_CHANNEL_SHUTDOWN && w->chand->resolver != NULL) {
       publish_state = GRPC_CHANNEL_TRANSIENT_FAILURE;
-      grpc_resolver_channel_saw_error(exec_ctx, w->chand->resolver);
+      grpc_resolver_channel_saw_error_locked(exec_ctx, w->chand->resolver);
       GRPC_LB_POLICY_UNREF(exec_ctx, w->chand->lb_policy, "channel");
       w->chand->lb_policy = NULL;
     }
@@ -386,11 +386,12 @@ static void on_resolver_result_changed_locked(grpc_exec_ctx *exec_ctx,
       watch_lb_policy(exec_ctx, chand, lb_policy, state);
     }
     GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
-    grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
-                       &chand->on_resolver_result_changed);
+    grpc_resolver_next_locked(exec_ctx, chand->resolver,
+                              &chand->resolver_result,
+                              &chand->on_resolver_result_changed);
   } else {
     if (chand->resolver != NULL) {
-      grpc_resolver_shutdown(exec_ctx, chand->resolver);
+      grpc_resolver_shutdown_locked(exec_ctx, chand->resolver);
       GRPC_RESOLVER_UNREF(exec_ctx, chand->resolver, "channel");
       chand->resolver = NULL;
     }
@@ -451,7 +452,7 @@ static void start_transport_op_locked(grpc_exec_ctx *exec_ctx, void *arg,
       set_channel_connectivity_state_locked(
           exec_ctx, chand, GRPC_CHANNEL_SHUTDOWN,
           GRPC_ERROR_REF(op->disconnect_with_error), "disconnect");
-      grpc_resolver_shutdown(exec_ctx, chand->resolver);
+      grpc_resolver_shutdown_locked(exec_ctx, chand->resolver);
       GRPC_RESOLVER_UNREF(exec_ctx, chand->resolver, "channel");
       chand->resolver = NULL;
       if (!chand->started_resolving) {
@@ -550,7 +551,7 @@ static grpc_error *cc_init_channel_elem(grpc_exec_ctx *exec_ctx,
   chand->resolver = grpc_resolver_create(
       exec_ctx, proxy_name != NULL ? proxy_name : arg->value.string,
       new_args != NULL ? new_args : args->channel_args,
-      chand->interested_parties);
+      chand->interested_parties, chand->combiner);
   if (proxy_name != NULL) gpr_free(proxy_name);
   if (new_args != NULL) grpc_channel_args_destroy(exec_ctx, new_args);
   if (chand->resolver == NULL) {
@@ -559,13 +560,23 @@ static grpc_error *cc_init_channel_elem(grpc_exec_ctx *exec_ctx,
   return GRPC_ERROR_NONE;
 }
 
+static void shutdown_resolver_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                     grpc_error *error) {
+  grpc_resolver *resolver = arg;
+  grpc_resolver_shutdown_locked(exec_ctx, resolver);
+  GRPC_RESOLVER_UNREF(exec_ctx, resolver, "channel");
+}
+
 /* Destructor for channel_data */
 static void cc_destroy_channel_elem(grpc_exec_ctx *exec_ctx,
                                     grpc_channel_element *elem) {
   channel_data *chand = elem->channel_data;
   if (chand->resolver != NULL) {
-    grpc_resolver_shutdown(exec_ctx, chand->resolver);
-    GRPC_RESOLVER_UNREF(exec_ctx, chand->resolver, "channel");
+    grpc_closure_sched(
+        exec_ctx,
+        grpc_closure_create(shutdown_resolver_locked, chand->resolver,
+                            grpc_combiner_scheduler(chand->combiner, false)),
+        GRPC_ERROR_NONE);
   }
   if (chand->client_channel_factory != NULL) {
     grpc_client_channel_factory_unref(exec_ctx, chand->client_channel_factory);
@@ -846,8 +857,9 @@ static bool pick_subchannel_locked(
   if (chand->resolver != NULL && !chand->started_resolving) {
     chand->started_resolving = true;
     GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
-    grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
-                       &chand->on_resolver_result_changed);
+    grpc_resolver_next_locked(exec_ctx, chand->resolver,
+                              &chand->resolver_result,
+                              &chand->on_resolver_result_changed);
   }
   if (chand->resolver != NULL) {
     cpa = gpr_malloc(sizeof(*cpa));
@@ -1210,8 +1222,9 @@ static void try_to_connect_locked(grpc_exec_ctx *exec_ctx, void *arg,
     if (!chand->started_resolving && chand->resolver != NULL) {
       GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
       chand->started_resolving = true;
-      grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
-                         &chand->on_resolver_result_changed);
+      grpc_resolver_next_locked(exec_ctx, chand->resolver,
+                                &chand->resolver_result,
+                                &chand->on_resolver_result_changed);
     }
   }
   GRPC_CHANNEL_STACK_UNREF(exec_ctx, chand->owning_stack, "try_to_connect");
diff --git a/src/core/ext/client_channel/resolver.c b/src/core/ext/client_channel/resolver.c
index 2ae4fe862e9..b1a1faa6c96 100644
--- a/src/core/ext/client_channel/resolver.c
+++ b/src/core/ext/client_channel/resolver.c
@@ -32,10 +32,13 @@
  */
 
 #include "src/core/ext/client_channel/resolver.h"
+#include "src/core/lib/iomgr/combiner.h"
 
 void grpc_resolver_init(grpc_resolver *resolver,
-                        const grpc_resolver_vtable *vtable) {
+                        const grpc_resolver_vtable *vtable,
+                        grpc_combiner *combiner) {
   resolver->vtable = vtable;
+  resolver->combiner = GRPC_COMBINER_REF(combiner, "resolver");
   gpr_ref_init(&resolver->refs, 1);
 }
 
@@ -62,20 +65,24 @@ void grpc_resolver_unref(grpc_resolver *resolver,
 void grpc_resolver_unref(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver) {
 #endif
   if (gpr_unref(&resolver->refs)) {
+    grpc_combiner *combiner = resolver->combiner;
     resolver->vtable->destroy(exec_ctx, resolver);
+    GRPC_COMBINER_UNREF(exec_ctx, combiner, "resolver");
   }
 }
 
-void grpc_resolver_shutdown(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver) {
-  resolver->vtable->shutdown(exec_ctx, resolver);
+void grpc_resolver_shutdown_locked(grpc_exec_ctx *exec_ctx,
+                                   grpc_resolver *resolver) {
+  resolver->vtable->shutdown_locked(exec_ctx, resolver);
 }
 
-void grpc_resolver_channel_saw_error(grpc_exec_ctx *exec_ctx,
-                                     grpc_resolver *resolver) {
-  resolver->vtable->channel_saw_error(exec_ctx, resolver);
+void grpc_resolver_channel_saw_error_locked(grpc_exec_ctx *exec_ctx,
+                                            grpc_resolver *resolver) {
+  resolver->vtable->channel_saw_error_locked(exec_ctx, resolver);
 }
 
-void grpc_resolver_next(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
-                        grpc_channel_args **result, grpc_closure *on_complete) {
-  resolver->vtable->next(exec_ctx, resolver, result, on_complete);
+void grpc_resolver_next_locked(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
+                               grpc_channel_args **result,
+                               grpc_closure *on_complete) {
+  resolver->vtable->next_locked(exec_ctx, resolver, result, on_complete);
 }
diff --git a/src/core/ext/client_channel/resolver.h b/src/core/ext/client_channel/resolver.h
index 96ece92b9d8..bbba424ca5d 100644
--- a/src/core/ext/client_channel/resolver.h
+++ b/src/core/ext/client_channel/resolver.h
@@ -44,14 +44,16 @@ typedef struct grpc_resolver_vtable grpc_resolver_vtable;
 struct grpc_resolver {
   const grpc_resolver_vtable *vtable;
   gpr_refcount refs;
+  grpc_combiner *combiner;
 };
 
 struct grpc_resolver_vtable {
   void (*destroy)(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver);
-  void (*shutdown)(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver);
-  void (*channel_saw_error)(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver);
-  void (*next)(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
-               grpc_channel_args **result, grpc_closure *on_complete);
+  void (*shutdown_locked)(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver);
+  void (*channel_saw_error_locked)(grpc_exec_ctx *exec_ctx,
+                                   grpc_resolver *resolver);
+  void (*next_locked)(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
+                      grpc_channel_args **result, grpc_closure *on_complete);
 };
 
 #ifdef GRPC_RESOLVER_REFCOUNT_DEBUG
@@ -70,21 +72,30 @@ void grpc_resolver_unref(grpc_exec_ctx *exec_ctx, grpc_resolver *policy);
 #endif
 
 void grpc_resolver_init(grpc_resolver *resolver,
-                        const grpc_resolver_vtable *vtable);
+                        const grpc_resolver_vtable *vtable,
+                        grpc_combiner *combiner);
 
-void grpc_resolver_shutdown(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver);
+void grpc_resolver_shutdown_locked(grpc_exec_ctx *exec_ctx,
+                                   grpc_resolver *resolver);
 
 /** Notification that the channel has seen an error on some address.
-    Can be used as a hint that re-resolution is desirable soon. */
-void grpc_resolver_channel_saw_error(grpc_exec_ctx *exec_ctx,
-                                     grpc_resolver *resolver);
+    Can be used as a hint that re-resolution is desirable soon.
+
+    Must be called from the combiner passed as a resolver_arg at construction
+    time.*/
+void grpc_resolver_channel_saw_error_locked(grpc_exec_ctx *exec_ctx,
+                                            grpc_resolver *resolver);
 
 /** Get the next result from the resolver.  Expected to set \a *result with
     new channel args and then schedule \a on_complete for execution.
 
     If resolution is fatally broken, set \a *result to NULL and
-    schedule \a on_complete. */
-void grpc_resolver_next(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
-                        grpc_channel_args **result, grpc_closure *on_complete);
+    schedule \a on_complete.
+
+    Must be called from the combiner passed as a resolver_arg at construction
+    time.*/
+void grpc_resolver_next_locked(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
+                               grpc_channel_args **result,
+                               grpc_closure *on_complete);
 
 #endif /* GRPC_CORE_EXT_CLIENT_CHANNEL_RESOLVER_H */
diff --git a/src/core/ext/client_channel/resolver_factory.h b/src/core/ext/client_channel/resolver_factory.h
index 3792ddca18c..e3cd99ec5a4 100644
--- a/src/core/ext/client_channel/resolver_factory.h
+++ b/src/core/ext/client_channel/resolver_factory.h
@@ -50,6 +50,7 @@ typedef struct grpc_resolver_args {
   grpc_uri *uri;
   const grpc_channel_args *args;
   grpc_pollset_set *pollset_set;
+  grpc_combiner *combiner;
 } grpc_resolver_args;
 
 struct grpc_resolver_factory_vtable {
diff --git a/src/core/ext/client_channel/resolver_registry.c b/src/core/ext/client_channel/resolver_registry.c
index 5110a7cad9e..f8e8bc9c393 100644
--- a/src/core/ext/client_channel/resolver_registry.c
+++ b/src/core/ext/client_channel/resolver_registry.c
@@ -133,7 +133,8 @@ static grpc_resolver_factory *resolve_factory(const char *target,
 
 grpc_resolver *grpc_resolver_create(grpc_exec_ctx *exec_ctx, const char *target,
                                     const grpc_channel_args *args,
-                                    grpc_pollset_set *pollset_set) {
+                                    grpc_pollset_set *pollset_set,
+                                    grpc_combiner *combiner) {
   grpc_uri *uri = NULL;
   char *canonical_target = NULL;
   grpc_resolver_factory *factory =
@@ -144,6 +145,7 @@ grpc_resolver *grpc_resolver_create(grpc_exec_ctx *exec_ctx, const char *target,
   resolver_args.uri = uri;
   resolver_args.args = args;
   resolver_args.pollset_set = pollset_set;
+  resolver_args.combiner = combiner;
   resolver =
       grpc_resolver_factory_create_resolver(exec_ctx, factory, &resolver_args);
   grpc_uri_destroy(uri);
diff --git a/src/core/ext/client_channel/resolver_registry.h b/src/core/ext/client_channel/resolver_registry.h
index a4606463ebd..e2c189cf0cd 100644
--- a/src/core/ext/client_channel/resolver_registry.h
+++ b/src/core/ext/client_channel/resolver_registry.h
@@ -65,7 +65,8 @@ void grpc_register_resolver_type(grpc_resolver_factory *factory);
     should not be NULL. */
 grpc_resolver *grpc_resolver_create(grpc_exec_ctx *exec_ctx, const char *target,
                                     const grpc_channel_args *args,
-                                    grpc_pollset_set *pollset_set);
+                                    grpc_pollset_set *pollset_set,
+                                    grpc_combiner *combiner);
 
 /** Find a resolver factory given a name and return an (owned-by-the-caller)
  *  reference to it */
diff --git a/src/core/ext/resolver/dns/native/dns_resolver.c b/src/core/ext/resolver/dns/native/dns_resolver.c
index c08b53ea040..96ac521a91b 100644
--- a/src/core/ext/resolver/dns/native/dns_resolver.c
+++ b/src/core/ext/resolver/dns/native/dns_resolver.c
@@ -40,6 +40,7 @@
 #include "src/core/ext/client_channel/lb_policy_registry.h"
 #include "src/core/ext/client_channel/resolver_registry.h"
 #include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/iomgr/combiner.h"
 #include "src/core/lib/iomgr/resolve_address.h"
 #include "src/core/lib/iomgr/timer.h"
 #include "src/core/lib/support/backoff.h"
@@ -63,8 +64,6 @@ typedef struct {
   /** pollset_set to drive the name resolution process */
   grpc_pollset_set *interested_parties;
 
-  /** mutex guarding the rest of the state */
-  gpr_mu mu;
   /** are we currently resolving? */
   bool resolving;
   /** which version of the result have we published? */
@@ -95,18 +94,20 @@ static void dns_start_resolving_locked(grpc_exec_ctx *exec_ctx,
 static void dns_maybe_finish_next_locked(grpc_exec_ctx *exec_ctx,
                                          dns_resolver *r);
 
-static void dns_shutdown(grpc_exec_ctx *exec_ctx, grpc_resolver *r);
-static void dns_channel_saw_error(grpc_exec_ctx *exec_ctx, grpc_resolver *r);
-static void dns_next(grpc_exec_ctx *exec_ctx, grpc_resolver *r,
-                     grpc_channel_args **target_result,
-                     grpc_closure *on_complete);
+static void dns_shutdown_locked(grpc_exec_ctx *exec_ctx, grpc_resolver *r);
+static void dns_channel_saw_error_locked(grpc_exec_ctx *exec_ctx,
+                                         grpc_resolver *r);
+static void dns_next_locked(grpc_exec_ctx *exec_ctx, grpc_resolver *r,
+                            grpc_channel_args **target_result,
+                            grpc_closure *on_complete);
 
 static const grpc_resolver_vtable dns_resolver_vtable = {
-    dns_destroy, dns_shutdown, dns_channel_saw_error, dns_next};
+    dns_destroy, dns_shutdown_locked, dns_channel_saw_error_locked,
+    dns_next_locked};
 
-static void dns_shutdown(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver) {
+static void dns_shutdown_locked(grpc_exec_ctx *exec_ctx,
+                                grpc_resolver *resolver) {
   dns_resolver *r = (dns_resolver *)resolver;
-  gpr_mu_lock(&r->mu);
   if (r->have_retry_timer) {
     grpc_timer_cancel(exec_ctx, &r->retry_timer);
   }
@@ -116,25 +117,21 @@ static void dns_shutdown(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver) {
                        GRPC_ERROR_CREATE("Resolver Shutdown"));
     r->next_completion = NULL;
   }
-  gpr_mu_unlock(&r->mu);
 }
 
-static void dns_channel_saw_error(grpc_exec_ctx *exec_ctx,
-                                  grpc_resolver *resolver) {
+static void dns_channel_saw_error_locked(grpc_exec_ctx *exec_ctx,
+                                         grpc_resolver *resolver) {
   dns_resolver *r = (dns_resolver *)resolver;
-  gpr_mu_lock(&r->mu);
   if (!r->resolving) {
     gpr_backoff_reset(&r->backoff_state);
     dns_start_resolving_locked(exec_ctx, r);
   }
-  gpr_mu_unlock(&r->mu);
 }
 
-static void dns_next(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
-                     grpc_channel_args **target_result,
-                     grpc_closure *on_complete) {
+static void dns_next_locked(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
+                            grpc_channel_args **target_result,
+                            grpc_closure *on_complete) {
   dns_resolver *r = (dns_resolver *)resolver;
-  gpr_mu_lock(&r->mu);
   GPR_ASSERT(!r->next_completion);
   r->next_completion = on_complete;
   r->target_result = target_result;
@@ -144,30 +141,26 @@ static void dns_next(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
   } else {
     dns_maybe_finish_next_locked(exec_ctx, r);
   }
-  gpr_mu_unlock(&r->mu);
 }
 
-static void dns_on_retry_timer(grpc_exec_ctx *exec_ctx, void *arg,
-                               grpc_error *error) {
+static void dns_on_retry_timer_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                      grpc_error *error) {
   dns_resolver *r = arg;
 
-  gpr_mu_lock(&r->mu);
   r->have_retry_timer = false;
   if (error == GRPC_ERROR_NONE) {
     if (!r->resolving) {
       dns_start_resolving_locked(exec_ctx, r);
     }
   }
-  gpr_mu_unlock(&r->mu);
 
   GRPC_RESOLVER_UNREF(exec_ctx, &r->base, "retry-timer");
 }
 
-static void dns_on_resolved(grpc_exec_ctx *exec_ctx, void *arg,
-                            grpc_error *error) {
+static void dns_on_resolved_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                   grpc_error *error) {
   dns_resolver *r = arg;
   grpc_channel_args *result = NULL;
-  gpr_mu_lock(&r->mu);
   GPR_ASSERT(r->resolving);
   r->resolving = false;
   if (r->addresses != NULL) {
@@ -198,8 +191,8 @@ static void dns_on_resolved(grpc_exec_ctx *exec_ctx, void *arg,
     } else {
       gpr_log(GPR_DEBUG, "retrying immediately");
     }
-    grpc_closure_init(&r->on_retry, dns_on_retry_timer, r,
-                      grpc_schedule_on_exec_ctx);
+    grpc_closure_init(&r->on_retry, dns_on_retry_timer_locked, r,
+                      grpc_combiner_scheduler(r->base.combiner, false));
     grpc_timer_init(exec_ctx, &r->retry_timer, next_try, &r->on_retry, now);
   }
   if (r->resolved_result != NULL) {
@@ -208,7 +201,6 @@ static void dns_on_resolved(grpc_exec_ctx *exec_ctx, void *arg,
   r->resolved_result = result;
   r->resolved_version++;
   dns_maybe_finish_next_locked(exec_ctx, r);
-  gpr_mu_unlock(&r->mu);
 
   GRPC_RESOLVER_UNREF(exec_ctx, &r->base, "dns-resolving");
 }
@@ -221,7 +213,8 @@ static void dns_start_resolving_locked(grpc_exec_ctx *exec_ctx,
   r->addresses = NULL;
   grpc_resolve_address(
       exec_ctx, r->name_to_resolve, r->default_port, r->interested_parties,
-      grpc_closure_create(dns_on_resolved, r, grpc_schedule_on_exec_ctx),
+      grpc_closure_create(dns_on_resolved_locked, r,
+                          grpc_combiner_scheduler(r->base.combiner, false)),
       &r->addresses);
 }
 
@@ -240,7 +233,6 @@ static void dns_maybe_finish_next_locked(grpc_exec_ctx *exec_ctx,
 
 static void dns_destroy(grpc_exec_ctx *exec_ctx, grpc_resolver *gr) {
   dns_resolver *r = (dns_resolver *)gr;
-  gpr_mu_destroy(&r->mu);
   if (r->resolved_result != NULL) {
     grpc_channel_args_destroy(exec_ctx, r->resolved_result);
   }
@@ -264,8 +256,7 @@ static grpc_resolver *dns_create(grpc_exec_ctx *exec_ctx,
   // Create resolver.
   dns_resolver *r = gpr_malloc(sizeof(dns_resolver));
   memset(r, 0, sizeof(*r));
-  gpr_mu_init(&r->mu);
-  grpc_resolver_init(&r->base, &dns_resolver_vtable);
+  grpc_resolver_init(&r->base, &dns_resolver_vtable, args->combiner);
   r->name_to_resolve = gpr_strdup(path);
   r->default_port = gpr_strdup(default_port);
   r->channel_args = grpc_channel_args_copy(args->args);
diff --git a/src/core/ext/resolver/sockaddr/sockaddr_resolver.c b/src/core/ext/resolver/sockaddr/sockaddr_resolver.c
index a1365f64656..e7f66649b5d 100644
--- a/src/core/ext/resolver/sockaddr/sockaddr_resolver.c
+++ b/src/core/ext/resolver/sockaddr/sockaddr_resolver.c
@@ -45,6 +45,7 @@
 #include "src/core/ext/client_channel/parse_address.h"
 #include "src/core/ext/client_channel/resolver_registry.h"
 #include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/iomgr/combiner.h"
 #include "src/core/lib/iomgr/resolve_address.h"
 #include "src/core/lib/iomgr/unix_sockets_posix.h"
 #include "src/core/lib/slice/slice_internal.h"
@@ -58,8 +59,6 @@ typedef struct {
   grpc_lb_addresses *addresses;
   /** channel args */
   grpc_channel_args *channel_args;
-  /** mutex guarding the rest of the state */
-  gpr_mu mu;
   /** have we published? */
   bool published;
   /** pending next completion, or NULL */
@@ -73,48 +72,43 @@ static void sockaddr_destroy(grpc_exec_ctx *exec_ctx, grpc_resolver *r);
 static void sockaddr_maybe_finish_next_locked(grpc_exec_ctx *exec_ctx,
                                               sockaddr_resolver *r);
 
-static void sockaddr_shutdown(grpc_exec_ctx *exec_ctx, grpc_resolver *r);
-static void sockaddr_channel_saw_error(grpc_exec_ctx *exec_ctx,
-                                       grpc_resolver *r);
-static void sockaddr_next(grpc_exec_ctx *exec_ctx, grpc_resolver *r,
-                          grpc_channel_args **target_result,
-                          grpc_closure *on_complete);
+static void sockaddr_shutdown_locked(grpc_exec_ctx *exec_ctx, grpc_resolver *r);
+static void sockaddr_channel_saw_error_locked(grpc_exec_ctx *exec_ctx,
+                                              grpc_resolver *r);
+static void sockaddr_next_locked(grpc_exec_ctx *exec_ctx, grpc_resolver *r,
+                                 grpc_channel_args **target_result,
+                                 grpc_closure *on_complete);
 
 static const grpc_resolver_vtable sockaddr_resolver_vtable = {
-    sockaddr_destroy, sockaddr_shutdown, sockaddr_channel_saw_error,
-    sockaddr_next};
+    sockaddr_destroy, sockaddr_shutdown_locked,
+    sockaddr_channel_saw_error_locked, sockaddr_next_locked};
 
-static void sockaddr_shutdown(grpc_exec_ctx *exec_ctx,
-                              grpc_resolver *resolver) {
+static void sockaddr_shutdown_locked(grpc_exec_ctx *exec_ctx,
+                                     grpc_resolver *resolver) {
   sockaddr_resolver *r = (sockaddr_resolver *)resolver;
-  gpr_mu_lock(&r->mu);
   if (r->next_completion != NULL) {
     *r->target_result = NULL;
     grpc_closure_sched(exec_ctx, r->next_completion, GRPC_ERROR_NONE);
     r->next_completion = NULL;
   }
-  gpr_mu_unlock(&r->mu);
 }
 
-static void sockaddr_channel_saw_error(grpc_exec_ctx *exec_ctx,
-                                       grpc_resolver *resolver) {
+static void sockaddr_channel_saw_error_locked(grpc_exec_ctx *exec_ctx,
+                                              grpc_resolver *resolver) {
   sockaddr_resolver *r = (sockaddr_resolver *)resolver;
-  gpr_mu_lock(&r->mu);
   r->published = false;
   sockaddr_maybe_finish_next_locked(exec_ctx, r);
-  gpr_mu_unlock(&r->mu);
 }
 
-static void sockaddr_next(grpc_exec_ctx *exec_ctx, grpc_resolver *resolver,
-                          grpc_channel_args **target_result,
-                          grpc_closure *on_complete) {
+static void sockaddr_next_locked(grpc_exec_ctx *exec_ctx,
+                                 grpc_resolver *resolver,
+                                 grpc_channel_args **target_result,
+                                 grpc_closure *on_complete) {
   sockaddr_resolver *r = (sockaddr_resolver *)resolver;
-  gpr_mu_lock(&r->mu);
   GPR_ASSERT(!r->next_completion);
   r->next_completion = on_complete;
   r->target_result = target_result;
   sockaddr_maybe_finish_next_locked(exec_ctx, r);
-  gpr_mu_unlock(&r->mu);
 }
 
 static void sockaddr_maybe_finish_next_locked(grpc_exec_ctx *exec_ctx,
@@ -131,7 +125,6 @@ static void sockaddr_maybe_finish_next_locked(grpc_exec_ctx *exec_ctx,
 
 static void sockaddr_destroy(grpc_exec_ctx *exec_ctx, grpc_resolver *gr) {
   sockaddr_resolver *r = (sockaddr_resolver *)gr;
-  gpr_mu_destroy(&r->mu);
   grpc_lb_addresses_destroy(exec_ctx, r->addresses);
   grpc_channel_args_destroy(exec_ctx, r->channel_args);
   gpr_free(r);
@@ -201,8 +194,7 @@ static grpc_resolver *sockaddr_create(grpc_exec_ctx *exec_ctx,
   memset(r, 0, sizeof(*r));
   r->addresses = addresses;
   r->channel_args = grpc_channel_args_copy(args->args);
-  gpr_mu_init(&r->mu);
-  grpc_resolver_init(&r->base, &sockaddr_resolver_vtable);
+  grpc_resolver_init(&r->base, &sockaddr_resolver_vtable, args->combiner);
   return &r->base;
 }
 
diff --git a/src/core/lib/surface/call.c b/src/core/lib/surface/call.c
index 48a1e586e17..0fae3effb63 100644
--- a/src/core/lib/surface/call.c
+++ b/src/core/lib/surface/call.c
@@ -101,6 +101,17 @@ typedef struct {
   grpc_error *error;
 } received_status;
 
+static gpr_atm pack_received_status(received_status r) {
+  return r.is_set ? (1 | (gpr_atm)r.error) : 0;
+}
+
+static received_status unpack_received_status(gpr_atm atm) {
+  return (atm & 1) == 0
+             ? (received_status){.is_set = false, .error = GRPC_ERROR_NONE}
+             : (received_status){.is_set = true,
+                                 .error = (grpc_error *)(atm & ~(gpr_atm)1)};
+}
+
 #define MAX_ERRORS_PER_BATCH 3
 
 typedef struct batch_control {
@@ -165,8 +176,8 @@ struct grpc_call {
      Element 0 is initial metadata, element 1 is trailing metadata. */
   grpc_metadata_array *buffered_metadata[2];
 
-  /* Received call statuses from various sources */
-  received_status status[STATUS_SOURCE_COUNT];
+  /* Packed received call statuses from various sources */
+  gpr_atm status[STATUS_SOURCE_COUNT];
 
   /* Call data useful used for reporting. Only valid after the call has
    * completed */
@@ -446,7 +457,8 @@ static void destroy_call(grpc_exec_ctx *exec_ctx, void *call,
       gpr_time_sub(gpr_now(GPR_CLOCK_MONOTONIC), c->start_time);
 
   for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
-    GRPC_ERROR_UNREF(c->status[i].error);
+    GRPC_ERROR_UNREF(
+        unpack_received_status(gpr_atm_no_barrier_load(&c->status[i])).error);
   }
 
   grpc_call_stack_destroy(exec_ctx, CALL_STACK_FROM_CALL(c), &c->final_info, c);
@@ -614,13 +626,12 @@ static void cancel_with_status(grpc_exec_ctx *exec_ctx, grpc_call *c,
  */
 
 static bool get_final_status_from(
-    grpc_call *call, status_source from_source, bool allow_ok_status,
+    grpc_call *call, grpc_error *error, bool allow_ok_status,
     void (*set_value)(grpc_status_code code, void *user_data),
     void *set_value_user_data, grpc_slice *details) {
   grpc_status_code code;
   const char *msg = NULL;
-  grpc_error_get_status(call->status[from_source].error, call->send_deadline,
-                        &code, &msg, NULL);
+  grpc_error_get_status(error, call->send_deadline, &code, &msg, NULL);
   if (code == GRPC_STATUS_OK && !allow_ok_status) {
     return false;
   }
@@ -638,12 +649,15 @@ static void get_final_status(grpc_call *call,
                                                void *user_data),
                              void *set_value_user_data, grpc_slice *details) {
   int i;
+  received_status status[STATUS_SOURCE_COUNT];
+  for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
+    status[i] = unpack_received_status(gpr_atm_acq_load(&call->status[i]));
+  }
   if (grpc_call_error_trace) {
     gpr_log(GPR_DEBUG, "get_final_status %s", call->is_client ? "CLI" : "SVR");
     for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
-      if (call->status[i].is_set) {
-        gpr_log(GPR_DEBUG, "  %d: %s", i,
-                grpc_error_string(call->status[i].error));
+      if (status[i].is_set) {
+        gpr_log(GPR_DEBUG, "  %d: %s", i, grpc_error_string(status[i].error));
       }
     }
   }
@@ -653,9 +667,9 @@ static void get_final_status(grpc_call *call,
     /* search for the best status we can present: ideally the error we use has a
        clearly defined grpc-status, and we'll prefer that. */
     for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
-      if (call->status[i].is_set &&
-          grpc_error_has_clear_grpc_status(call->status[i].error)) {
-        if (get_final_status_from(call, (status_source)i, allow_ok_status != 0,
+      if (status[i].is_set &&
+          grpc_error_has_clear_grpc_status(status[i].error)) {
+        if (get_final_status_from(call, status[i].error, allow_ok_status != 0,
                                   set_value, set_value_user_data, details)) {
           return;
         }
@@ -663,8 +677,8 @@ static void get_final_status(grpc_call *call,
     }
     /* If no clearly defined status exists, search for 'anything' */
     for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
-      if (call->status[i].is_set) {
-        if (get_final_status_from(call, (status_source)i, allow_ok_status != 0,
+      if (status[i].is_set) {
+        if (get_final_status_from(call, status[i].error, allow_ok_status != 0,
                                   set_value, set_value_user_data, details)) {
           return;
         }
@@ -681,12 +695,13 @@ static void get_final_status(grpc_call *call,
 
 static void set_status_from_error(grpc_exec_ctx *exec_ctx, grpc_call *call,
                                   status_source source, grpc_error *error) {
-  if (call->status[source].is_set) {
+  if (!gpr_atm_rel_cas(&call->status[source],
+                       pack_received_status((received_status){
+                           .is_set = false, .error = GRPC_ERROR_NONE}),
+                       pack_received_status((received_status){
+                           .is_set = true, .error = error}))) {
     GRPC_ERROR_UNREF(error);
-    return;
   }
-  call->status[source].is_set = true;
-  call->status[source].error = error;
 }
 
 /*******************************************************************************
diff --git a/test/core/client_channel/resolvers/dns_resolver_connectivity_test.c b/test/core/client_channel/resolvers/dns_resolver_connectivity_test.c
index cfd37052de4..3e3401165cd 100644
--- a/test/core/client_channel/resolvers/dns_resolver_connectivity_test.c
+++ b/test/core/client_channel/resolvers/dns_resolver_connectivity_test.c
@@ -36,14 +36,17 @@
 #include <grpc/grpc.h>
 #include <grpc/support/alloc.h>
 
+#include "src/core/ext/client_channel/resolver.h"
 #include "src/core/ext/client_channel/resolver_registry.h"
 #include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/iomgr/combiner.h"
 #include "src/core/lib/iomgr/resolve_address.h"
 #include "src/core/lib/iomgr/timer.h"
 #include "test/core/util/test_config.h"
 
 static gpr_mu g_mu;
 static bool g_fail_resolution = true;
+static grpc_combiner *g_combiner;
 
 static grpc_error *my_resolve_address(const char *name, const char *addr,
                                       grpc_resolved_addresses **addrs) {
@@ -71,6 +74,7 @@ static grpc_resolver *create_resolver(grpc_exec_ctx *exec_ctx,
   grpc_resolver_args args;
   memset(&args, 0, sizeof(args));
   args.uri = uri;
+  args.combiner = g_combiner;
   grpc_resolver *resolver =
       grpc_resolver_factory_create_resolver(exec_ctx, factory, &args);
   grpc_resolver_factory_unref(factory);
@@ -96,11 +100,41 @@ static bool wait_loop(int deadline_seconds, gpr_event *ev) {
   return false;
 }
 
+typedef struct next_args {
+  grpc_resolver *resolver;
+  grpc_channel_args **result;
+  grpc_closure *on_complete;
+} next_args;
+
+static void call_resolver_next_now_lock_taken(grpc_exec_ctx *exec_ctx,
+                                              void *arg,
+                                              grpc_error *error_unused) {
+  next_args *a = arg;
+  grpc_resolver_next_locked(exec_ctx, a->resolver, a->result, a->on_complete);
+  gpr_free(a);
+}
+
+static void call_resolver_next_after_locking(grpc_exec_ctx *exec_ctx,
+                                             grpc_resolver *resolver,
+                                             grpc_channel_args **result,
+                                             grpc_closure *on_complete) {
+  next_args *a = gpr_malloc(sizeof(*a));
+  a->resolver = resolver;
+  a->result = result;
+  a->on_complete = on_complete;
+  grpc_closure_sched(
+      exec_ctx,
+      grpc_closure_create(call_resolver_next_now_lock_taken, a,
+                          grpc_combiner_scheduler(resolver->combiner, false)),
+      GRPC_ERROR_NONE);
+}
+
 int main(int argc, char **argv) {
   grpc_test_init(argc, argv);
 
   grpc_init();
   gpr_mu_init(&g_mu);
+  g_combiner = grpc_combiner_create(NULL);
   grpc_blocking_resolve_address = my_resolve_address;
   grpc_channel_args *result = (grpc_channel_args *)1;
 
@@ -108,7 +142,7 @@ int main(int argc, char **argv) {
   grpc_resolver *resolver = create_resolver(&exec_ctx, "dns:test");
   gpr_event ev1;
   gpr_event_init(&ev1);
-  grpc_resolver_next(
+  call_resolver_next_after_locking(
       &exec_ctx, resolver, &result,
       grpc_closure_create(on_done, &ev1, grpc_schedule_on_exec_ctx));
   grpc_exec_ctx_flush(&exec_ctx);
@@ -117,7 +151,7 @@ int main(int argc, char **argv) {
 
   gpr_event ev2;
   gpr_event_init(&ev2);
-  grpc_resolver_next(
+  call_resolver_next_after_locking(
       &exec_ctx, resolver, &result,
       grpc_closure_create(on_done, &ev2, grpc_schedule_on_exec_ctx));
   grpc_exec_ctx_flush(&exec_ctx);
@@ -126,6 +160,7 @@ int main(int argc, char **argv) {
 
   grpc_channel_args_destroy(&exec_ctx, result);
   GRPC_RESOLVER_UNREF(&exec_ctx, resolver, "test");
+  GRPC_COMBINER_UNREF(&exec_ctx, g_combiner, "test");
   grpc_exec_ctx_finish(&exec_ctx);
 
   grpc_shutdown();
diff --git a/test/core/client_channel/resolvers/dns_resolver_test.c b/test/core/client_channel/resolvers/dns_resolver_test.c
index 5603a57b5fc..9dd5aed0919 100644
--- a/test/core/client_channel/resolvers/dns_resolver_test.c
+++ b/test/core/client_channel/resolvers/dns_resolver_test.c
@@ -36,8 +36,11 @@
 #include <grpc/support/log.h>
 
 #include "src/core/ext/client_channel/resolver_registry.h"
+#include "src/core/lib/iomgr/combiner.h"
 #include "test/core/util/test_config.h"
 
+static grpc_combiner *g_combiner;
+
 static void test_succeeds(grpc_resolver_factory *factory, const char *string) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   grpc_uri *uri = grpc_uri_parse(string, 0);
@@ -48,6 +51,7 @@ static void test_succeeds(grpc_resolver_factory *factory, const char *string) {
   GPR_ASSERT(uri);
   memset(&args, 0, sizeof(args));
   args.uri = uri;
+  args.combiner = g_combiner;
   resolver = grpc_resolver_factory_create_resolver(&exec_ctx, factory, &args);
   GPR_ASSERT(resolver != NULL);
   GRPC_RESOLVER_UNREF(&exec_ctx, resolver, "test_succeeds");
@@ -65,6 +69,7 @@ static void test_fails(grpc_resolver_factory *factory, const char *string) {
   GPR_ASSERT(uri);
   memset(&args, 0, sizeof(args));
   args.uri = uri;
+  args.combiner = g_combiner;
   resolver = grpc_resolver_factory_create_resolver(&exec_ctx, factory, &args);
   GPR_ASSERT(resolver == NULL);
   grpc_uri_destroy(uri);
@@ -76,6 +81,8 @@ int main(int argc, char **argv) {
   grpc_test_init(argc, argv);
   grpc_init();
 
+  g_combiner = grpc_combiner_create(NULL);
+
   dns = grpc_resolver_factory_lookup("dns");
 
   test_succeeds(dns, "dns:10.2.1.1");
@@ -84,6 +91,11 @@ int main(int argc, char **argv) {
   test_fails(dns, "ipv4://8.8.8.8/8.8.8.8:8888");
 
   grpc_resolver_factory_unref(dns);
+  {
+    grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+    GRPC_COMBINER_UNREF(&exec_ctx, g_combiner, "test");
+    grpc_exec_ctx_finish(&exec_ctx);
+  }
   grpc_shutdown();
 
   return 0;
diff --git a/test/core/client_channel/resolvers/sockaddr_resolver_test.c b/test/core/client_channel/resolvers/sockaddr_resolver_test.c
index 10df78537c8..68831ab7c79 100644
--- a/test/core/client_channel/resolvers/sockaddr_resolver_test.c
+++ b/test/core/client_channel/resolvers/sockaddr_resolver_test.c
@@ -39,9 +39,12 @@
 
 #include "src/core/ext/client_channel/resolver_registry.h"
 #include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/iomgr/combiner.h"
 
 #include "test/core/util/test_config.h"
 
+static grpc_combiner *g_combiner;
+
 typedef struct on_resolution_arg {
   char *expected_server_name;
   grpc_channel_args *resolver_result;
@@ -62,6 +65,7 @@ static void test_succeeds(grpc_resolver_factory *factory, const char *string) {
   GPR_ASSERT(uri);
   memset(&args, 0, sizeof(args));
   args.uri = uri;
+  args.combiner = g_combiner;
   resolver = grpc_resolver_factory_create_resolver(&exec_ctx, factory, &args);
   GPR_ASSERT(resolver != NULL);
 
@@ -71,8 +75,8 @@ static void test_succeeds(grpc_resolver_factory *factory, const char *string) {
   grpc_closure *on_resolution = grpc_closure_create(
       on_resolution_cb, &on_res_arg, grpc_schedule_on_exec_ctx);
 
-  grpc_resolver_next(&exec_ctx, resolver, &on_res_arg.resolver_result,
-                     on_resolution);
+  grpc_resolver_next_locked(&exec_ctx, resolver, &on_res_arg.resolver_result,
+                            on_resolution);
   GRPC_RESOLVER_UNREF(&exec_ctx, resolver, "test_succeeds");
   grpc_exec_ctx_finish(&exec_ctx);
   grpc_uri_destroy(uri);
@@ -88,6 +92,7 @@ static void test_fails(grpc_resolver_factory *factory, const char *string) {
   GPR_ASSERT(uri);
   memset(&args, 0, sizeof(args));
   args.uri = uri;
+  args.combiner = g_combiner;
   resolver = grpc_resolver_factory_create_resolver(&exec_ctx, factory, &args);
   GPR_ASSERT(resolver == NULL);
   grpc_uri_destroy(uri);
@@ -99,6 +104,8 @@ int main(int argc, char **argv) {
   grpc_test_init(argc, argv);
   grpc_init();
 
+  g_combiner = grpc_combiner_create(NULL);
+
   ipv4 = grpc_resolver_factory_lookup("ipv4");
   ipv6 = grpc_resolver_factory_lookup("ipv6");
 
@@ -118,6 +125,12 @@ int main(int argc, char **argv) {
 
   grpc_resolver_factory_unref(ipv4);
   grpc_resolver_factory_unref(ipv6);
+
+  {
+    grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+    GRPC_COMBINER_UNREF(&exec_ctx, g_combiner, "test");
+    grpc_exec_ctx_finish(&exec_ctx);
+  }
   grpc_shutdown();
 
   return 0;
diff --git a/test/core/end2end/fake_resolver.c b/test/core/end2end/fake_resolver.c
index 4f05f69f01f..8a37531449e 100644
--- a/test/core/end2end/fake_resolver.c
+++ b/test/core/end2end/fake_resolver.c
@@ -213,7 +213,7 @@ static grpc_resolver* fake_resolver_create(grpc_exec_ctx* exec_ctx,
   r->channel_args = grpc_channel_args_copy(args->args);
   r->addresses = addresses;
   gpr_mu_init(&r->mu);
-  grpc_resolver_init(&r->base, &fake_resolver_vtable);
+  grpc_resolver_init(&r->base, &fake_resolver_vtable, args->combiner);
   return &r->base;
 }