diff --git a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um.c b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um.c
index fecedc98ed..b370122120 100755
--- a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um.c
+++ b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um.c
@@ -449,7 +449,7 @@ rlc_um_mac_status_indication (void *rlc_pP, frame_t frameP, eNB_flag_t eNB_flagP
       status_resp.rlc_info.rlc_protocol_state = ((rlc_um_entity_t *) rlc_pP)->protocol_state;
       #ifdef DEBUG_RLC_UM_TX_STATUS
       if ((((rlc_um_entity_t *) rlc_pP)->rb_id > 0) && (status_resp.buffer_occupancy_in_bytes > 0)) {
-          LOG_D(RLC, "[FRAME %05d][%s][RLC_UM][MOD %02u/%02u][RB %02d] MAC_STATUS_INDICATION (DATA) %d bytes -> %d bytes\n",
+          LOG_D(RLC, "[FRAME %05d][%s][RLC_UM][MOD %02u/%02u][RB %02d] MAC_STATUS_INDICATION (DATA) %d bytes requested -> %d bytes available\n",
                   frameP,
                   (rlc_p->is_enb) ? "eNB" : "UE",
                   rlc_p->enb_module_id,
@@ -479,7 +479,7 @@ rlc_um_mac_status_indication (void *rlc_pP, frame_t frameP, eNB_flag_t eNB_flagP
       }
       #endif
   } else {
-     LOG_E(RLC, "[RLC] RLCp not defined!!!\n");
+     LOG_E(RLC, "[RLC] rlc_um_mac_status_indication RLC NULL!!!\n");
   }
   return status_resp;
 }
@@ -709,7 +709,9 @@ rlc_um_data_req (void *rlc_pP, frame_t frameP, mem_block_t *sdu_pP)
       LOG_T(RLC, "%s", message_string);
 #endif 
 #   endif
+      pthread_mutex_lock(&rlc_p->lock_input_sdus);
       list_add_tail_eurecom(sdu_pP, &rlc_p->input_sdus);
+      pthread_mutex_unlock(&rlc_p->lock_input_sdus);
 
   /*} else {
     LOG_W(RLC, "[FRAME %05d][%s][RLC_UM][MOD %02u/%02u][RB %02d] RLC-UM_DATA_REQ input buffer full SDU garbaged\n",
diff --git a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_control_primitives.c b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_control_primitives.c
index 953c225b05..63ecce9b5a 100755
--- a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_control_primitives.c
+++ b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_control_primitives.c
@@ -240,6 +240,7 @@ rlc_um_init (rlc_um_entity_t * const rlc_pP)
       memset (rlc_pP, 0, sizeof (rlc_um_entity_t));
       // TX SIDE
       list_init (&rlc_pP->pdus_to_mac_layer, NULL);
+      pthread_mutex_init(&rlc_pP->lock_input_sdus, NULL);
       list_init (&rlc_pP->input_sdus, NULL);
 
       rlc_pP->protocol_state = RLC_NULL_STATE;
@@ -291,6 +292,7 @@ rlc_um_cleanup (rlc_um_entity_t * const rlc_pP)
   int             index;
   // TX SIDE
   list_free (&rlc_pP->pdus_to_mac_layer);
+  pthread_mutex_destroy(&rlc_pP->lock_input_sdus);
   list_free (&rlc_pP->input_sdus);
 
   // RX SIDE
diff --git a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_entity.h b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_entity.h
index c0c509fa64..b890822166 100755
--- a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_entity.h
+++ b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_entity.h
@@ -38,6 +38,7 @@
 #    ifndef __RLC_UM_ENTITY_H__
 #        define __RLC_UM_ENTITY_H__
 
+#        include <pthread.h>
 #        include "platform_types.h"
 #        include "platform_constants.h"
 #        include "list.h"
@@ -93,6 +94,8 @@ typedef struct rlc_um_entity_s {
   // tranmission
   //-----------------------------
   // sdu communication;
+  //pthread_spinlock_t lock_input_sdus;
+  pthread_mutex_t      lock_input_sdus;
   list_t               input_sdus;                /*!< \brief Input SDU buffer (for SDUs coming from upper layers). Should be accessed as an array. */
   rlc_buffer_occupancy_t buffer_occupancy;          /*!< \brief Number of bytes contained in input_sdus buffer.*/
   uint32_t             nb_bytes_requested_by_mac; /*!< \brief Number of bytes requested by lower layer for next transmission. */
diff --git a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_segment.c b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_segment.c
index 2ff96d0fea..7d09a6c14a 100755
--- a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_segment.c
+++ b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_segment.c
@@ -99,6 +99,8 @@ rlc_um_segment_10 (rlc_um_entity_t *rlc_pP,frame_t frameP)
     list_init (&pdus, NULL);    // param string identifying the list is NULL
     pdu_mem_p = NULL;
 
+    // not fine locking
+    pthread_mutex_lock(&rlc_pP->lock_input_sdus);
     while ((list_get_head(&rlc_pP->input_sdus)) && (nb_bytes_to_transmit > 0)) {
 
 #if defined(TRACE_RLC_UM_SEGMENT)
@@ -150,6 +152,7 @@ rlc_um_segment_10 (rlc_um_entity_t *rlc_pP,frame_t frameP)
                         rlc_pP->ue_module_id,
                         rlc_pP->rb_id);
 #endif
+                pthread_mutex_unlock(&rlc_pP->lock_input_sdus);
                 return;
             }
 #if defined(TRACE_RLC_UM_SEGMENT)
@@ -483,6 +486,7 @@ rlc_um_segment_10 (rlc_um_entity_t *rlc_pP,frame_t frameP)
         //nb_bytes_to_transmit = nb_bytes_to_transmit - data_pdu_size;
         nb_bytes_to_transmit = 0; // 1 PDU only
     }
+    pthread_mutex_unlock(&rlc_pP->lock_input_sdus);
 }
 //-----------------------------------------------------------------------------
 void
@@ -540,6 +544,7 @@ rlc_um_segment_5 (rlc_um_entity_t *rlc_pP,frame_t frameP)
     list_init (&pdus, NULL);    // param string identifying the list is NULL
     pdu_mem_p = NULL;
 
+    pthread_mutex_lock(&rlc_pP->lock_input_sdus);
     while ((list_get_head(&rlc_pP->input_sdus)) && (nb_bytes_to_transmit > 0)) {
 #if defined(TRACE_RLC_UM_SEGMENT)
         LOG_D(RLC, "[FRAME %05u][%s][RLC_UM][MOD %u/%u][RB %u] SEGMENT5 nb_bytes_to_transmit %d BO %d\n",
@@ -590,6 +595,7 @@ rlc_um_segment_5 (rlc_um_entity_t *rlc_pP,frame_t frameP)
                         rlc_pP->ue_module_id,
                         rlc_pP->rb_id);
 #endif
+                pthread_mutex_unlock(&rlc_pP->lock_input_sdus);
                 return;
             }
 #if defined(TRACE_RLC_UM_SEGMENT)
@@ -919,5 +925,6 @@ rlc_um_segment_5 (rlc_um_entity_t *rlc_pP,frame_t frameP)
         //nb_bytes_to_transmit = nb_bytes_to_transmit - data_pdu_size;
         nb_bytes_to_transmit = 0; // 1 PDU only
     }
+    pthread_mutex_unlock(&rlc_pP->lock_input_sdus);
 }