PDCP DL handling: unlock PDCP before forwarding PDU

nr_pdcp_entity_recv_sdu() processes PDCP SDUs, and forwards the PDU at the
end of the function, while having the PDCP lock. This can lead to
deadlocks, e.g., when another thread goes through RLC and tries to
access the PDCP while the PDCP tries to lock the RLC.

This commit changes the logic: instead of having recv_sdu() forward the
PDU directly, it fills a buffer with the PDU (thus the name change to
process_sdu()), and returns. We then unlock the PDCP, before forwarding
the PDU, thus eliminating potential deadlocks.

openair2/SDAP/nr_sdap/nr_sdap_entity.c

@@ -39,11 +39,18 @@ instance_t *N3GTPUInst = NULL;
 
 void nr_pdcp_submit_sdap_ctrl_pdu(ue_id_t ue_id, rb_id_t sdap_ctrl_pdu_drb, nr_sdap_ul_hdr_t ctrl_pdu)
 {
-  nr_pdcp_ue_t *ue;
-  nr_pdcp_ue_manager_t *nr_pdcp_ue_manager;
-  nr_pdcp_ue_manager = nr_pdcp_sdap_get_ue_manager();
-  ue = nr_pdcp_manager_get_ue(nr_pdcp_ue_manager, ue_id);
-  ue->drb[sdap_ctrl_pdu_drb-1]->recv_sdu(ue->drb[sdap_ctrl_pdu_drb-1], (char*)&ctrl_pdu, SDAP_HDR_LENGTH, RLC_MUI_UNDEFINED);
+
+  protocol_ctxt_t ctxt = { .rntiMaybeUEid = ue_id };
+  nr_pdcp_data_req_drb(&ctxt,
+                       SRB_FLAG_NO,
+                       sdap_ctrl_pdu_drb,
+                       RLC_MUI_UNDEFINED,
+                       SDU_CONFIRM_NO,
+                       SDAP_HDR_LENGTH,
+                       (unsigned char *)&ctrl_pdu,
+                       PDCP_TRANSMISSION_MODE_UNKNOWN,
+                       NULL,
+                       NULL);
   LOG_D(SDAP, "Control PDU - Submitting Control PDU to DRB ID:  %ld\n", sdap_ctrl_pdu_drb);
   LOG_D(SDAP, "QFI: %u\n R: %u\n D/C: %u\n", ctrl_pdu.QFI, ctrl_pdu.R, ctrl_pdu.DC);
   return;