diff --git a/lib/aos/aos_rpc.c b/lib/aos/aos_rpc.c
index 4a08083..69e0ac5 100644
--- a/lib/aos/aos_rpc.c
+++ b/lib/aos/aos_rpc.c
@@ -38,11 +38,12 @@ static errval_t do_aos_rpc(
     // allocate capability if we expect one and the recv slot is empty
     if (ret_cap != NULL && rpc->chan->endpoint->k.recv_cptr == 0){
         lmp_chan_alloc_recv_slot(rpc->chan);
+        assert(rpc->chan->endpoint->k.recv_cptr != 0);
     }
 
     // Send call
     while (true) {
-        err = lmp_chan_send4(rpc->chan, LMP_FLAG_YIELD | LMP_FLAG_SYNC, arg_cap, msg_type, arg_size, arg0, arg1);
+        err = lmp_chan_send4(rpc->chan, LMP_FLAG_YIELD, arg_cap, msg_type, arg_size, arg0, arg1);
         if (!err_is_fail(err)) break;
         if (!lmp_err_is_transient(err)) {
             return err_push(err, AOS_ERR_LMP_SEND_FAILURE);
@@ -77,7 +78,7 @@ aos_rpc_send_number(struct aos_rpc *rpc, uintptr_t num) {
     // given channel and wait until the ack gets returned.
     errval_t err;
 
-    thread_mutex_lock_nested(&rpc->lock);
+    thread_mutex_lock(&rpc->lock);
     err = do_aos_rpc(
         rpc, RPC_MTYPE_SEND_NUMBER,
         NULL_CAP, 0, num, 0,
@@ -96,7 +97,7 @@ aos_rpc_send_string(struct aos_rpc *rpc, const char *string) {
     size_t string_size = strlen(string) + 1;
     if (string_size > RPC_SHARED_SIZE) return AOS_ERR_RPC_ARG_TOO_BIG;
 
-    thread_mutex_lock_nested(&rpc->lock);
+    thread_mutex_lock(&rpc->lock);
     memcpy(rpc->shared_mem, string, string_size);
     err = do_aos_rpc(
         rpc, RPC_MTYPE_SEND_STRING,
@@ -123,7 +124,7 @@ aos_rpc_get_ram_cap(struct aos_rpc *rpc, size_t bytes, size_t alignment,
         ret_cap, NULL, ret_bytes, NULL
     );
     thread_mutex_unlock(&rpc->lock);
-
+    
     return err;
 }
 
@@ -135,7 +136,7 @@ aos_rpc_serial_getchar(struct aos_rpc *rpc, char *retc) {
     errval_t err;
     uintptr_t retval;
 
-    thread_mutex_lock_nested(&rpc->lock);
+    thread_mutex_lock(&rpc->lock);
     err = do_aos_rpc(
         rpc, RPC_MTYPE_SERIAL_GETCHAR,
         NULL_CAP, 0, 0, 0,
@@ -153,7 +154,7 @@ aos_rpc_serial_putchar(struct aos_rpc *rpc, char c) {
     // serial port.
     errval_t err;
 
-    thread_mutex_lock_nested(&rpc->lock);
+    thread_mutex_lock(&rpc->lock);
     err = do_aos_rpc(
         rpc, RPC_MTYPE_SERIAL_PUTCHAR,
         NULL_CAP, 0, c, 0,
@@ -176,7 +177,7 @@ aos_rpc_serial_write(struct aos_rpc *rpc, const char *buf, size_t buf_len) {
         size_t chunk_len = MIN(buf_len, RPC_SHARED_SIZE);
         size_t written_bytes;
 
-        thread_mutex_lock_nested(&rpc->lock);
+        thread_mutex_lock(&rpc->lock);
         memcpy(rpc->shared_mem, buf, chunk_len);
         err = do_aos_rpc(
             rpc, RPC_MTYPE_SERIAL_WRITE,
@@ -217,7 +218,7 @@ aos_rpc_serial_read(struct aos_rpc *rpc, char *buf, size_t buf_len) {
         size_t chunk_len = MIN(buf_len, RPC_SHARED_SIZE);
         size_t read_bytes;
 
-        thread_mutex_lock_nested(&rpc->lock);
+        thread_mutex_lock(&rpc->lock);
         err = do_aos_rpc(
             rpc, RPC_MTYPE_SERIAL_READ,
             NULL_CAP, 0, chunk_len, 0,
@@ -253,7 +254,7 @@ aos_rpc_process_spawn(struct aos_rpc *rpc, char *cmdline,
     size_t cmdline_size = strlen(cmdline) + 1;
     if (cmdline_size > RPC_SHARED_SIZE) return AOS_ERR_RPC_ARG_TOO_BIG;
 
-    thread_mutex_lock_nested(&rpc->lock);
+    thread_mutex_lock(&rpc->lock);
     memcpy(rpc->shared_mem, cmdline, cmdline_size);
     uintptr_t retval;
     errval_t err = do_aos_rpc(
@@ -275,7 +276,7 @@ aos_rpc_process_get_name(struct aos_rpc *rpc, domainid_t pid, char **name) {
     size_t name_len;
     errval_t err;
 
-    thread_mutex_lock_nested(&rpc->lock);
+    thread_mutex_lock(&rpc->lock);
     err = do_aos_rpc(
         rpc, RPC_MTYPE_PROCESS_GET_NAME,
         NULL_CAP, 0, pid, 0,
@@ -301,7 +302,7 @@ aos_rpc_process_get_all_pids(struct aos_rpc *rpc, domainid_t **pids,
     size_t ret_len;
     errval_t err;
 
-    thread_mutex_lock_nested(&rpc->lock);
+    thread_mutex_lock(&rpc->lock);
     err = do_aos_rpc(
         rpc, RPC_MTYPE_PROCESS_GET_ALL_PIDS,
         NULL_CAP, 0, 0, 0,