On Mon, 10 Jul 2017 17:59:17 -0700 John Fastabend <john.fastab...@gmail.com> wrote:
> On 07/10/2017 11:30 AM, Jesper Dangaard Brouer wrote: > > On Sat, 8 Jul 2017 21:06:17 +0200 > > Jesper Dangaard Brouer <bro...@redhat.com> wrote: > > > >> On Sat, 08 Jul 2017 10:46:18 +0100 (WEST) > >> David Miller <da...@davemloft.net> wrote: > >> > >>> From: John Fastabend <john.fastab...@gmail.com> > >>> Date: Fri, 07 Jul 2017 10:48:36 -0700 > >>> > >>>> On 07/07/2017 10:34 AM, John Fastabend wrote: > >>>>> This series adds two new XDP helper routines bpf_redirect() and > >>>>> bpf_redirect_map(). The first variant bpf_redirect() is meant > >>>>> to be used the same way it is currently being used by the cls_bpf > >>>>> classifier. An xdp packet will be redirected immediately when this > >>>>> is called. > >>>> > >>>> Also other than the typo in the title there ;) I'm going to CC > >>>> the driver maintainers working on XDP (makes for a long CC list but) > >>>> because we would want to try and get support in as many as possible in > >>>> the next merge window. > >>>> > >>>> For this rev I just implemented on ixgbe because I wrote the > >>>> original XDP support there. I'll volunteer to do virtio as well. > >>> > >>> I went over this series a few times and it looks great to me. > >>> You didn't even give me some coding style issues to pick on :-) > >> > >> We (Daniel, Andy and I) have been reviewing and improving on this > >> patchset the last couple of weeks ;-). We had some stability issues, > >> which is why it wasn't published earlier. My plan is to test this > >> latest patchset again, Monday and Tuesday. I'll try to assess stability > >> and provide some performance numbers. > > > > > > Damn, I though it was stable, I have been running a lot of performance > > tests, and then this just happened :-( > > Thanks, I'll take a look through the code and see if I can come up with > why this might happen. I haven't hit it on my tests yet though. I've figured out why this happens, and I have a fix, see patch below with some comments with questions. The problem is that we can leak map_to_flush in an error path, the fix: diff --git a/net/core/filter.c b/net/core/filter.c index 2ccd6ff09493..7f1f48668dcf 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2497,11 +2497,14 @@ int xdp_do_redirect_map(struct net_device *dev, struct xdp_buff *xdp, ri->map = NULL; trace_xdp_redirect(dev, fwd, xdp_prog, XDP_REDIRECT); - + // Q: Should we also trace "goto out" (failed lookup)? + // like bpf_warn_invalid_xdp_redirect(); return __bpf_tx_xdp(fwd, map, xdp, index); out: ri->ifindex = 0; - ri->map = NULL; + // XXX: here we could leak ri->map_to_flush, which could be + // picked up later by xdp_do_flush_map() + xdp_do_flush_map(); /* Clears ri->map_to_flush + ri->map */ return -EINVAL; While debugging this, I noticed that we can have packets in-flight, while the XDP RX rings are being reconfigured. I wonder if this is a ixgbe driver XDP-bug? I think it would be best to add some RCU-barrier, after ixgbe_setup_tc(). diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c index ed97aa81a850..4872fbb54ecd 100644 --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c @@ -9801,7 +9804,18 @@ static int ixgbe_xdp_setup(struct net_device *dev, struct bpf_prog *prog) /* If transitioning XDP modes reconfigure rings */ if (!!prog != !!old_prog) { - int err = ixgbe_setup_tc(dev, netdev_get_num_tc(dev)); + // XXX: Warn pkts can be in-flight in old_prog + // while ixgbe_setup_tc() calls ixgbe_close(dev). + // + // Should we avoid these in-flight packets? + // Would it be enough to add an synchronize_rcu() + // or rcu_barrier()? + // or do we need an napi_synchronize() call here? + // + int err; + netdev_info(dev, + "Calling ixgbe_setup_tc() to reconfig XDP rings\n"); + err = ixgbe_setup_tc(dev, netdev_get_num_tc(dev)); if (err) { rcu_assign_pointer(adapter->xdp_prog, old_prog); -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer