[En-Nut-Discussion] Possible race condition in DHCP and DHCPKick
hmnews at proconx.com
Fri Feb 10 06:39:44 CET 2012
it appears that there is a race condition in DHCP, routine DhcpKick():
I observed cases where the following sequence would cause a system
lock-up because the NutEventWait/dhcpDone condition is never fullfilled.
Some debugging and analysis of the order of events sent and received
between the caller and DHCP thread shows, that there are cases where
NutEventPost does a context switch and the dhcpDone event is sent
before(!) NutEventWait(&dhcpDone) is called resulting the subsequent
call of NutEventWait(&dhcpDone) to never return.
The issue seems to be fixed once above NutEventPost is changed to a
NutEventPostAsync which avoids the context switch before NutEventWait is
If there are no objections or further insight into this topic, I would
submit a bug report to tracker and a patch.
I think in most applications DhcpKick is only called once during system
start and the issue does not come up. But if a system changes from DHCP
to statically allocated IP addresses or vice versa, DhcpKick is called
on every change and the issue comes to surface.
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