Re: [lwip-users] DHCP not surviving multiple reconnections

[Sylvain Rochet]

Hello,

On Wed, Feb 17, 2021 at 07:40:45PM +0100, goldsimon@gmx.de wrote:
> Am 16.02.2021 um 15:55 schrieb matt swindell:
> > Hello,
> >
> >  
> >
> > I am new to LWIP currently I am using LWIP 2.1.2 with no OS (NO_SYS = 1)
> > in lwipopts.h.
> >
> >  
> >
> > My question is about the connection/disconnection from the DHCP server.
> > Using Wireshark I am able to see the initial DHCP request and properly
> > receive an IP address, followed by ARP announcements. The device seems
> > to survive an initial disconnect, sending a Request to validate it’s IP
> > and an ACK from the DHCP server once reconnected. However, further
> > disconnects and reconnections appear to confuse the device.
> >
> >  
> >
> > I have a PHY interrupt callback which calls netif_set_link_down() and
> > netif_set_link_up() when the PHY link status changes. Since the dhcp
> > state was bound dhcp_reboot() is called from dhcp_network_changed().
> > This all seems to work fine until we hit the dhcp_timeout() and my dhcp
> > tries are greater than or equal to REBOOT_TRIES, at which point it calls
> > dhcp_discover() and I get stuck in a loop where the device sends a
> > discovery message and is offered an IP address back but it gets ignored.
> >
> >  
> >
> > By increasing REBOOT_TRIES I am able to get a few more reconnections
> > without problem, but at some point it always seems to get stuck in that
> > dhcp discovery loop.
> >
> >  
> >
> > I am unsure if I have done something incorrectly or if I am confusing
> > the DHCP state machine, but from everything I have read with regards to
> > LWIP > 2.x.x
> >
> > calling netif_set_link_up/down() should be sufficient for maintaining
> > DHCP once dhcp_start() has been called.
> >
> >  
> >
> > Any help would be greatly appreciated.
> 
> I'm not aware of a bug here, but I'm not sure. It would probably be best
> if you could reproduce this with a unit test?

I am not sure it is the problem but at least from the description it 
looks like netif_set_link_down() and netif_set_link_up() are being 
called in interrupt context, which is probably wrong unless the lwIP 
main loop is guarded by a huge and ugly critical section.

Sylvain

signature.asc
Description: Digital signature