[LU-13779] Correct asymmetric route detection

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.15.0
• Severity: 3
• Assignee: Chris Horn
• Reporter: Chris Horn

Description

In lnet_parse():

        if (lnet_drop_asym_route && for_me &&
            LNET_NIDNET(src_nid) != LNET_NIDNET(from_nid)) {
                struct lnet_net *net;
                struct lnet_remotenet *rnet;
                bool found = true;
...
                rnet = lnet_find_rnet_locked(LNET_NIDNET(src_nid));
                if (rnet) {
...
                }
                lnet_net_unlock(cpt);
                if (!found) {
...
                        goto drop;

Failure to lookup the remote net for LNET_NIDNET(src_nid) indicates an asymmetric route, but we do not drop the message in this case.

another problem with this code: there's no guarantee that we'll have a route->lr_lnet that matches the net of ni->ni_nid.

It would be better to move this check to after we have looked up the lpni of from_nid. Then, we can look at just the routes associated with the gateway that owns the lpni. If one of those routes has lr_net == LNET_NIDNET(src_nid), then the route is symmetrical