Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx> writes: > On Thu, Mar 25, 2021 at 12:38:07AM +0100, Toke Høiland-Jørgensen wrote: >> Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx> writes: >> >> > On Mon, Mar 22, 2021 at 10:47:09PM +0100, Toke Høiland-Jørgensen wrote: >> >> Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx> writes: >> >> >> >> > Currently, if there are multiple xdpsock instances running on a single >> >> > interface and in case one of the instances is terminated, the rest of >> >> > them are left in an inoperable state due to the fact of unloaded XDP >> >> > prog from interface. >> >> > >> >> > Consider the scenario below: >> >> > >> >> > // load xdp prog and xskmap and add entry to xskmap at idx 10 >> >> > $ sudo ./xdpsock -i ens801f0 -t -q 10 >> >> > >> >> > // add entry to xskmap at idx 11 >> >> > $ sudo ./xdpsock -i ens801f0 -t -q 11 >> >> > >> >> > terminate one of the processes and another one is unable to work due to >> >> > the fact that the XDP prog was unloaded from interface. >> >> > >> >> > To address that, step away from setting bpf prog in favour of bpf_link. >> >> > This means that refcounting of BPF resources will be done automatically >> >> > by bpf_link itself. >> >> > >> >> > Provide backward compatibility by checking if underlying system is >> >> > bpf_link capable. Do this by looking up/creating bpf_link on loopback >> >> > device. If it failed in any way, stick with netlink-based XDP prog. >> >> > Otherwise, use bpf_link-based logic. >> >> >> >> So how is the caller supposed to know which of the cases happened? >> >> Presumably they need to do their own cleanup in that case? AFAICT you're >> >> changing the code to always clobber the existing XDP program on detach >> >> in the fallback case, which seems like a bit of an aggressive change? :) >> > >> > Sorry Toke, I was offline yesterday. >> > Yeah once again I went too far and we shouldn't do: >> > >> > bpf_set_link_xdp_fd(xsk->ctx->ifindex, -1, 0); >> > >> > if xsk_lookup_bpf_maps(xsk) returned non-zero value which implies that the >> > underlying prog is not AF_XDP related. >> > >> > closing prog_fd (and link_fd under the condition that system is bpf_link >> > capable) is enough for that case. >> >> I think the same thing goes for further down? With your patch, if the >> code takes the else branch (after checking prog_id), and then ends up >> going to err_set_bpf_maps, it'll now also do an unconditional >> bpf_set_link_xdp_fd(), where before it was checking prog_id again and >> only unloading if it previously loaded the program... > > Hmm it's messy, I think we need a bit of refactoring here. Note that old > code was missing a close on ctx->xsks_map_fd if there was an error on > xsk_set_bpf_maps(xsk) and prog_id != 0 - given that > xsk_lookup_bpf_maps(xsk) succeeded, we therefore have a valid map fd that > we need to take care of on error path, for !prog_id case it was taken care > of within xsk_delete_bpf_maps(xsk). > > So how about a diff below (on top of this patch), where we separate paths > based on prog_id value retrieved earlier? xsk_set_bpf_maps(xsk) is > repeated but this way I feel like it's more clear with cleanup/error > paths. > > Wdyt? Yeah, that's much easier to follow! Nice :) -Toke
