[En-Nut-Discussion] Race condition and stack overflow in tcpsm.c

[Harald Kipp]

Hi Philipp,

On 14.11.2014 18:04, Philipp Burch wrote:
> Me again. More debugging showed that:
> 
> 1. 388 for tcpsm is still too less, I managed to make it use up to 664
> bytes and hence increased the stack space to 1024 bytes.
> 2. The DHCP thread overflowed as well, I had to set this to 1024 bytes
> as well.

Not sure if you are aware of

http://lists.egnite.de/pipermail/en-nut-discussion/2009-April/024939.html

Also the software manual

http://www.ethernut.de/pdf/enswm28e.pdf

gives some hints for debugging (page 46ff). It usually lets you
determine the required stack size.


> With these changes, I still managed to crash the system after some time,
> but it looks like a different problem this time, as all stacks should
> still be intact.

In the first place you need to find out, where it crashes, then why it
does. Yeah, I know, simply said but difficult to do. With ARM7 I was
quite successful with stack back-tracing. I do not have much experience
with Cortex, though.


> My testing is as follows:
> - Copy a file of some Megabytes to the SD card using FTP.
> - Send 2'000'000 flooding pings to the board with a preload of 10.
> - Issue 100'000 commands over three Telnet connections in parallel.

And, as long as you do this separately, all went well? It's quite useful
to check the system's reliability by stressing it this way, but it is
probably not useful for tracking problems.

While ping flooding and Telnet communication is tested often, not many
applications use FTP and FAT on SD-cards. Thus, it is more likely that
these parts fail.


> Always increasing the stacks doesn't seem like an appropriate solution
> however, I'd rather like to find out why the whole thing needs so much
> more space than on other platforms. Does anyone have an idea?

AFAIK, Nut/OS doesn't use recursive calls. So, stack requirements should
be deterministic and cannot grow beyond a specific limit.

Anyway, keep me informed about any progress.


Regards,

Harald