[PMTUd] fix external API and PMTUd interaction
The problem:
PMTUd can take a long time to release the global read lock, mostly due
to the pthread_cond_timedwait required to ack/nack packets from the
other hosts. This delay could block any wrlock operation for several seconds
if not more.
The solution:
each call to the global pthread_rwlock_wrlock has been changed to a wrapper
that will notify the PMTUd to interrupt its operations (and restart) first,
then get a global write lock that is queued as soon as PMTUd is going out.
This solution also improves a lot shutdown speed.
How to test:
This is not super simple to test and verify. I used 2 VMs with known MTU of
- Start knet_bench on both (normal ping_data -C is more than enough).
Once they have established data exchange, change the MTU on one of the nodes
to 1600 (or higher). This should guarantee that the PMTUd process will take
a very long time to complete.
First verify that the PMTUd process takes several seconds.
Once the next PMTUd run starts, hit ctrl+c on the node that is executing
the PMTUd and the process should exit much faster than before this patch.
Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>