packet_buffer_reserve() causes fault during long term test

[choehyunho]

Hi teams,

I am developing with Mesh SDK 4.0.0, and suffers from random fault during long-term test.

The last readable callstack position is the below.

NRF_MESH_ASSERT(m_get_packet(p_buffer, p_buffer->head)->packet_state !=
                    PACKET_BUFFER_MEM_STATE_RESERVED);

The callstack is QDEC_IRQHandler() -> bearer_event_handler() -> flag_event_cb() -> fire_timers() -> iv_update_timer_handler() -> iv_update_timeout_counter_store() -> mesh_config_entry_set() -> entry_store() -> dirty_entries_process() -> mesh_config_backend_store() -> mesh_config_backend_record_write() -> flash_manager_entry_alloc() -> reserve_action_buffer() -> packet_buffer_reserve()

This device is heavily loaded to send some data gathered from mesh network to local ethernet.

I am not sure exactly what kind of exception happens because I am not so familiar to SEGGER embedded studio.

Can someone explain what is the above error, and give some advice how to debug it?

[choehyunho]

I hope some reliable way to send logs to UART for Mesh SDK in the next release.

Using UART in mesh devices becomes unstable easily in current version.

Thank you for supporting.

[dave g]

Nordic bug: When a task calls packet_buffer_reserve() then packet_buffer_commit(),
if a timer ISR fires between those two task calls, and that ISR does the same thing
i.e. calls packet_buffer_reserve() then packet_buffer_commit(), then the ISR will assert,
because the main task has not yet advanced p_buffer->head, so the head block is already reserved.

[dave g]

For example, if the normal task calls mesh_gatt_packet_alloc(), and then before this
task calls mesh_gatt_packet_send(), a timer fires and the ISR callback calls proxy.c->
gatt_evt_handler->beacon_cycle_send->beacon_packet_send->packet_alloc->mesh_gatt_packet_alloc,
since both mesh_gatt_packet_alloc() instances call packet_buffer_reserve() with the
same packet buffer, the ISR will assert because the head is still in the reserved state.