gcoap/esp8266: Stack overflow with gcoap example

[kb2ma]

Description

The gcoap example app experiences a stack overflow when running on board esp8266-esp-12x. This issue arose due to stack use from #13386, which rebased gcoap's use of the sock library on the sock_async feature. For the lwIP stack, also depends on #13427 which added sock_async for lwIP.

Steps to reproduce the issue

There is a problem with stack use both with the GNRC networking stack and with the lwIP sock stack. However, the issue manifests itself differently for each stack. The problem is more acute with the lwIP stack.

To reproduce, build the gcoap example with DEVELHELP=0. Send a request to a server. Then accept a request from a client.

Expected results

Should be able to repeatedly send/receive messages.

Actual results

For GNRC, works as expected. However, the ps command (with DEVELHELP=1) shows the stack overflow. Notice that after send/receive, stack use is 1108 bytes out of 1108 available. If you rebuild with GCOAP_STACK_SIZE set for example to 2048, stack use is 1152 bytes.

For lwIP, the app receives and displays the response from the server. After receiving the request from the client, the board displays something like:

   EXCEPTION!! exccause=28 (LoadProhibitedCause) @4023782a excvaddr=00000004

The board then will reboot after about 30 seconds.

Versions

For GNRC, use RIOT master. For lwIP, use gcoap/lwip_async_support branch, which includes #13427 for lwip sock_async.

Detailed Measurements

The table below shows stack use after sending a /time request to libcoap example and receiving a /riot/board request.

> coap get -c fd00:bbbb::1 5683 /time
$ ./coap-client -m get -T 5a -U coap://[fd00:bbbb::2]/riot/board

"samr21" is for samr21-xpro board. "esp8266" is for esp8266-esp-12x board.

On samr21-xpro and esp8266-esp-12x, GCOAP_STACK_SIZE is 1108: 1024 from THREAD_STACKSIZE DEFAULT + 84 from sizeof(coap_pkt_t). We increased GCOAP_STACK_SIZE to 2048 for the esp8266 builds.

Using RIOT master 6dd69e7, 2019-02-29, which includes the gcoap adaptation to sock_async in #13386. esp8266 lwIP values using gcoap/lwip_async_support branch, based on RIOT master 2cc3d38, 2020-03-08, which includes #13427.

thread	samr21 ethos	samr21 6lo	esp8266 GNRC	esp8266 lwIP
isr_stack	208	168	344	344
idle	160	156	240	240
main	980	932	1396	2000
ipv6	568	624	804
udp	356	360	508
coap	816	740	1152	1648 (1)
ethos	564
6lo		468
at86rf2xx		608
netif-esp-wifi			920
ppT			1320	1320
pmT			328	328
rtT			1388	1388
esp_events			892	892
lwip_netdev_mux				448
tcpip_thread				1244
SUM	3652	4056	9392	9852

(1) Stack use is 1156 bytes after sending the GET to libcoap, and then increases to 1648 after receiving the GET from libcoap.

[kb2ma]

The stack size for gcoap on esp8266 is not sufficient. Presently GCOAP_STACK_SIZE is 1108. How to address? @gschorcht, I'd appreciate your thoughts.

1. esp32 uses 2048 for THREAD_STACKSIZE_DEFAULT. Increase the default for esp8266?

2. Set GCOAP_STACK_SIZE to 1536 (GNRC) or 2048 (lwIP) in esp8266 cpu_conf.h when the respective module is present? Stack size for GNRC IPv6 thread is set this way. Or set the value in gcoap.h based on CPU?

3. Create a GCOAP_STACKSIZE_EXTRA and set that to 0 by default, but 512 (GNRC) or 1024 (lwIP) in esp8266 cpu_conf.h?

[gschorcht]

@kb2ma I would prefer option 2. Increasing the default stack size could lead to insufficient memory for other applications if a lot of threads are created.

[kb2ma]

I would prefer option 2

Sounds good to me. I plan to create PRs to incorporate the changes from the gcoap/lwip_async_support branch as well as the increase to GCOAP_STACK_SIZE for esp8266.

[maribu]

Is this still an issue? Bumping the stack size should be easy enough