Re: [lwip-users] Resource starvation

[Simon Goldschmidt]

Honestly, I haven't thought too much about removing netifs since I regarded 
them quite static in embedded systems. However, I guess when removing a netif, 
we should have to do the same as when we change a local IP address (unless 
maybe a user wants to exchange netifs?)...

Simon


Yoav Nissim <address@hidden> wrote:

> 
> 
> Hello All,
> 
> 
> We have encountered a problem when removing netif's and would like to
> confirm the issue, and discuss ways of resolving it.
> 
> We are working with 1.4.0 rc1.
> 
> 
> The problem:
> 
> We have many situations in which network interfaces are brought down
> [and back up again], during normal processing of application (sockets)
> traffic.
> 
> This also happens implicitly every time a PPP connection is disconnected
> [and connected] as well.
> 
> We've found that after several such iterations, lwIP will have consumed
> its pbuf pool or its tcp_seg pool, and not recover.
> 
> Looking through the code showed that there are no paths that inform ip,
> tcp, or layers above that they cannot communicate anymore, and that they
> should clean up their state.
> 
> These connections seem to continue living, hogging resources until none
> are left.
> 
> 
> Could anyone confirm that this is indeed an issue?
> 
> 
> 
> The only "fix" we have found for now, lies in netif_set_ipaddr.
> 
> According to
> http://mail.gnu.org/archive/html/lwip-users/2003-03/msg00118.html, this
> function has code that cleans up active TCP PCBs that are bound to the
> interface's address.
> 
> When netif_remove() is called, we call netif_set_ipaddr with IPADDR_ANY
> to have the relevant TCP connections removed.
> 
> 
> This raises several questions:
> 
> 1. Is there a reason netif_remove() does not have such code?
> 
> 2. Assuming netif_remove() should have it, should netif_set_down() use
> it as well?
> 
> 3. Are there any other components that have to have their state cleaned
> up (IP, ARP, DNS, UDP, etc)?
> 
> 4. Assuming netif_remove() requires this cleanup, is this the right way
> to do it or is there a better way?
> 
> 5. What do we do with the listening PCBs? in netif_set_ipaddr, their
> bound addresses are simply changed to the new interface IP address. In
> netif_remove() they should probably be disposed of.
> 
> 
> 
> Appreciate your input,
> 
> Yoav.
> 
> 
> 
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