Re: [lwip-users] LWIP - TCP receive assert failed

[Sylvain Rochet]

Hello Jackie,

On Fri, Jan 16, 2015 at 09:47:06PM +0100, address@hidden wrote:
> Jackie:
> > After stress test and debugging, more than 10 hours uploading
> > data, I found the PCB got corrupt in tcp_output(). The case is
> > that tcp_output() can be blocked by the lower-level function call
> > in tcp_output_segment(), in which somehow the buffer of
> > lower-layer protocol is full, so the upper-layer is pending, and
> > at the same time, tcp timer is running,  tcp_slowtmr() is also
> > calling tcp_output(), so this tcp_output() is called before the
> 
> There you got the bug: when lwIP's threading requirements are
> observed, this can't happen: tcp_output() can never be called twice
> and thus does not have to be designed reentrant.
> 
> What you describe tells us that timers are checked from a different
> execution thread (thread or ISR) than output. But for the core lwIP
> code, you have to ensure this doesn't happen. That's all.

Indeed…

Jackie: please discard my previous mail, however I told you to check 
first if threading requirements are respected ;-)  (I know this isn't 
easy to do on third-party software.)

This is sad that an insane amount of reported bugs are about threading 
issues, this made me cringe about the overall code quality in shipped 
embedded devices.

Sylvain

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