Hello Jackie,
On Thu, Jan 22, 2015 at 10:36:17PM +0800, Jackie wrote:
Hi Simon & Sylvain,
After re-examining the code, finally I got more understanding of what
can cause this problem. Instead of more than one threads are calling
tcp_output(), there is only one thread tcpip_thread(), but in which
tcp_output() is called recursively.
The case happens when the lower-layer protocol (PPP) uses
sys_sem_wait(). In this function, it is not only waiting a semaphore,
but it also gives the timer chances to run. As long as it times out, the
tcp timer will be called, and in the timer, tcp_output() will be called
again, like,
tcpip_thread()
{
...
tcp_input()
{
...
tcp_output()
{
...
pppifOutput()
{
...
sys_sem_wait(); // Here the tcp_slowtmr() has a chance
to run again and tcp_output() may be called again in it.
Which PPP function is actually calling sys_sem_wait() ?
@Sylvain,
You are right, this PPP protocol implementation is from a third party,
Well, the "third party" for master is actually me.
so that I am not allowed to modify it so much.
Of course you are, not fixing a bug because the software is third party
does not make sense, not at all.
But I think this design is quite buggy, and the worst case is
tcp_output() can be called recursively several times.
Yes, it looks buggy :)
Sylvain
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