Re: cm_process_routed_req() does not resonate well with RoCE systems

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> On 18 Mar 2021, at 20:21, Haakon Bugge <haakon.bugge@xxxxxxxxxx> wrote:
> 
> With the introduction of RoCE systems, a CM REQ message will contain (pasted from Wireshark):
> 
> Primary Hop Limit: 0x40
> .... 0... = Primary Subnet Local: 0x0
> 
> This because cma_resolve_iboe_route() has:
> 
>        if (((struct sockaddr *)&id_priv->id.route.addr.dst_addr)->sa_family != AF_IB)
>                /* TODO: get the hoplimit from the inet/inet6 device */
>                route->path_rec->hop_limit = addr->dev_addr.hoplimit;
>        else
>                route->path_rec->hop_limit = 1;
> 
> The addr->dev_addr.hoplimit is coming from addr4_resolve(), which has:
> 
> 	addr->hoplimit = ip4_dst_hoplimit(&rt->dst);
> 
> ip4_dst_hoplimit() returns the value of the sysctl net.ipv4.ip_default_ttl in this case (64).
> 
> For the purpose of this case, consider the CM REQ to have the Primary SL != 0.
> 
> When this REQ gets processed by cm_req_handler(), the cm_process_routed_req() function is called.
> 
> Since the Primary Subnet Local value is zero in the request, and since this is RoCE (Primary Local LID is permissive), the following statement will be executed:
> 
> 	IBA_SET(CM_REQ_PRIMARY_SL, req_msg, wc->sl);
> 
> At least on the system I ran on, which was equipped with a Mellanox CX-5 HCA, the wc->sl is zero. Hence, the request to setup a connection using an SL != zero, will not be honoured, and a connection using SL zero will be created instead.
> 
> As a side note, in cm_process_routed_req(), we have:
> 
> 	IBA_SET(CM_REQ_PRIMARY_REMOTE_PORT_LID, req_msg, wc->dlid_path_bits);
> 
> which is strange, since a LID is 16 bits, whereas dlid_path_bits is only eight.
> 
> I am uncertain about the correct fix here. Any input appreciated.

I intend to send a patch doing:

--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -2138,7 +2138,8 @@ static int cm_req_handler(struct cm_work *work)
                goto destroy;
        }
 
-       cm_process_routed_req(req_msg, work->mad_recv_wc->wc);
+       if (cm_id_priv->av.ah_attr.type != RDMA_AH_ATTR_TYPE_ROCE)
+               cm_process_routed_req(req_msg, work->mad_recv_wc->wc);
 
        memset(&work->path[0], 0, sizeof(work->path[0]));
        if (cm_req_has_alt_path(req_msg))



if I do not get a push back.



Thxs, Håkon





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