Subject: Re: [PATCHv10 bpf-next 2/4] xdp: extend xdp_redirect_map with broadcast support

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 26 Apr 2021 13:41:05 +0200

On Mon, 26 Apr 2021 18:47:04 +0800
Hangbin Liu <[email-masked]> wrote:

> On Mon, Apr 26, 2021 at 11:53:50AM +0200, Jesper Dangaard Brouer wrote:
> > On Fri, 23 Apr 2021 10:00:17 +0800
> > Hangbin Liu <[email-masked]> wrote:
> >   
> > > This patch adds two flags BPF_F_BROADCAST and BPF_F_EXCLUDE_INGRESS to
> > > extend xdp_redirect_map for broadcast support.
> > > 
> > > With BPF_F_BROADCAST the packet will be broadcasted to all the interfaces
> > > in the map. with BPF_F_EXCLUDE_INGRESS the ingress interface will be
> > > excluded when do broadcasting.
> > > 
> > > When getting the devices in dev hash map via dev_map_hash_get_next_key(),
> > > there is a possibility that we fall back to the first key when a device
> > > was removed. This will duplicate packets on some interfaces. So just walk
> > > the whole buckets to avoid this issue. For dev array map, we also walk the
> > > whole map to find valid interfaces.
> > > 
> > > Function bpf_clear_redirect_map() was removed in
> > > commit ee75aef23afe ("bpf, xdp: Restructure redirect actions").
> > > Add it back as we need to use ri->map again.
> > > 
> > > Here is the performance result by using 10Gb i40e NIC, do XDP_DROP on
> > > veth peer, run xdp_redirect_{map, map_multi} in sample/bpf and send pkts
> > > via pktgen cmd:
> > > ./pktgen_sample03_burst_single_flow.sh -i eno1 -d $dst_ip -m $dst_mac -t 10 -s 64  
> > 
> > While running:
> >  $ sudo ./xdp_redirect_map_multi -F i40e2 i40e2
> >  Get interfaces 7 7
> >  libbpf: elf: skipping unrecognized data section(23) .eh_frame
> >  libbpf: elf: skipping relo section(24) .rel.eh_frame for section(23) .eh_frame
> >  Forwarding   10140845 pkt/s
> >  Forwarding   11767042 pkt/s
> >  Forwarding   11783437 pkt/s
> >  Forwarding   11767331 pkt/s
> > 
> > When starting:  sudo ./xdp_monitor --stats  
> 
> That seems the same issue I reported previously in our meeting.
> https://bugzilla.redhat.com/show_bug.cgi?id=1906820#c4
> 
> I only saw it 3 times and can't reproduce it easily.
> 
> Do you have any idea where is the root cause?

All the information you need to find the root-cause is listed below.
I have even decoded where in the code it happens, and also include the
code with line-numbering and pointed to the line the crash happens in,
I don't think it is possible for me to be more specific and help further.

> > System crashed with:
> > 
> > [ 5509.997837] BUG: kernel NULL pointer dereference, address: 0000000000000000
> > [ 5510.004793] #PF: supervisor read access in kernel mode
> > [ 5510.009929] #PF: error_code(0x0000) - not-present page
> > [ 5510.015060] PGD 0 P4D 0 
> > [ 5510.017591] Oops: 0000 [#1] PREEMPT SMP PTI
> > [ 5510.021769] CPU: 3 PID: 29 Comm: ksoftirqd/3 Not tainted 5.12.0-rc7-net-next-hangbin-v10+ #602
> > [ 5510.030368] Hardware name: Supermicro Super Server/X10SRi-F, BIOS 2.0a 08/01/2016
> > [ 5510.037835] RIP: 0010:perf_trace_xdp_redirect_template+0xba/0x130
> > [ 5510.043929] Code: 00 00 00 8b 45 18 74 1e 41 83 f9 19 74 18 45 85 c9 0f 85 83 00 00 00 81 7d 10 ff ff ff 7f 75 7a 89 c1 31 c0 eb 0d 48 8b 75 b8 <48> 8b 16 8b 8a d0 00 00 00 49 8b 55 38 41 b8 01 00 00 00 be 24 00
> > [ 5510.062668] RSP: 0018:ffffc9000017fc50 EFLAGS: 00010246
> > [ 5510.067884] RAX: 0000000000000000 RBX: ffffe8ffffccf180 RCX: 0000000000000000
> > [ 5510.075007] RDX: ffffffff817d1a9b RSI: 0000000000000000 RDI: ffffe8ffffcd8000
> > [ 5510.082133] RBP: ffffc9000017fc98 R08: 0000000000000000 R09: 0000000000000019
> > [ 5510.089256] R10: 0000000000000000 R11: ffff88887fd2ab70 R12: 0000000000000000
> > [ 5510.096382] R13: ffffc900000a5000 R14: ffff88810a8f2000 R15: ffffffff82a7c840
> > [ 5510.103505] FS:  0000000000000000(0000) GS:ffff88887fcc0000(0000) knlGS:0000000000000000
> > [ 5510.111584] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 5510.117319] CR2: 0000000000000000 CR3: 0000000157b1e004 CR4: 00000000003706e0
> > [ 5510.124444] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [ 5510.131567] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > [ 5510.138692] Call Trace:
> > [ 5510.141141]  xdp_do_redirect+0x16b/0x230
> > [ 5510.145064]  i40e_clean_rx_irq+0x62e/0x9a0 [i40e]
> > [ 5510.149779]  i40e_napi_poll+0xf0/0x410 [i40e]
> > [ 5510.154135]  __napi_poll+0x2a/0x140
> > [ 5510.157620]  net_rx_action+0x215/0x2d0
> > [ 5510.161364]  __do_softirq+0xe3/0x2df
> > [ 5510.164938]  run_ksoftirqd+0x1a/0x20
> > [ 5510.168514]  smpboot_thread_fn+0xee/0x1e0
> > [ 5510.172519]  ? sort_range+0x20/0x20
> > [ 5510.176003]  kthread+0x116/0x150
> > [ 5510.179237]  ? kthread_park+0x90/0x90
> > [ 5510.182893]  ret_from_fork+0x22/0x30
> > [ 5510.186474] Modules linked in: algif_hash af_alg bpf_preload fuse veth nf_defrag_ipv6 nf_defrag_ipv4 tun bridge stp llc rpcrdma sunrpc rdma_ucm ib_umad rdma_cm ib_ipoib coretemp iw_cm kvm_intel ib_cm kvm mlx5_ib i40iw irqbypass ib_uverbs rapl intel_cstate i2c_i801 intel_uncore ib_core pcspkr bfq i2c_smbus acpi_ipmi wmi ipmi_si ipmi_devintf ipmi_msghandler acpi_pad sch_fq_codel mlx5_core mlxfw i40e ixgbe igc psample mdio igb sd_mod ptp t10_pi nfp i2c_algo_bit i2c_core pps_core hid_generic [last unloaded: bpfilter]
> > [ 5510.231847] CR2: 0000000000000000
> > [ 5510.235164] ---[ end trace b8e076677c53b5e8 ]---
> > [ 5510.241762] RIP: 0010:perf_trace_xdp_redirect_template+0xba/0x130
> > [ 5510.247851] Code: 00 00 00 8b 45 18 74 1e 41 83 f9 19 74 18 45 85 c9 0f 85 83 00 00 00 81 7d 10 ff ff ff 7f 75 7a 89 c1 31 c0 eb 0d 48 8b 75 b8 <48> 8b 16 8b 8a d0 00 00 00 49 8b 55 38 41 b8 01 00 00 00 be 24 00
> > [ 5510.266590] RSP: 0018:ffffc9000017fc50 EFLAGS: 00010246
> > [ 5510.271804] RAX: 0000000000000000 RBX: ffffe8ffffccf180 RCX: 0000000000000000
> > [ 5510.278931] RDX: ffffffff817d1a9b RSI: 0000000000000000 RDI: ffffe8ffffcd8000
> > [ 5510.286053] RBP: ffffc9000017fc98 R08: 0000000000000000 R09: 0000000000000019
> > [ 5510.293178] R10: 0000000000000000 R11: ffff88887fd2ab70 R12: 0000000000000000
> > [ 5510.300301] R13: ffffc900000a5000 R14: ffff88810a8f2000 R15: ffffffff82a7c840
> > [ 5510.307426] FS:  0000000000000000(0000) GS:ffff88887fcc0000(0000) knlGS:0000000000000000
> > [ 5510.315503] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 5510.321241] CR2: 0000000000000000 CR3: 0000000157b1e004 CR4: 00000000003706e0
> > [ 5510.328364] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [ 5510.335490] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > [ 5510.342612] Kernel panic - not syncing: Fatal exception in interrupt
> > [ 5510.348994] Kernel Offset: disabled
> > [ 5510.354469] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---
> > 
> > [net-next]$ ./scripts/faddr2line vmlinux xdp_do_redirect+0x16b
> > xdp_do_redirect+0x16b/0x230:
> > trace_xdp_redirect at include/trace/events/xdp.h:136
> > (inlined by) trace_xdp_redirect at include/trace/events/xdp.h:136
> > (inlined by) xdp_do_redirect at net/core/filter.c:3996
> > 
> > Decode: perf_trace_xdp_redirect_template+0xba
> >  ./scripts/faddr2line vmlinux perf_trace_xdp_redirect_template+0xba
> > perf_trace_xdp_redirect_template+0xba/0x130:
> > perf_trace_xdp_redirect_template at include/trace/events/xdp.h:89 (discriminator 13)
> > 
> > less -N net/core/filter.c
> >  [...]
> >    3993         if (unlikely(err))
> >    3994                 goto err;
> >    3995   
> > -> 3996         _trace_xdp_redirect_map(dev, xdp_prog, fwd, map_type, map_id, ri->tgt_index);  
> >    3997         return 0;
> >    3998 err:
> >    3999         _trace_xdp_redirect_map_err(dev, xdp_prog, fwd, map_type, map_id, ri->tgt_index, err);
> >    4000         return err;
> >    4001 }
> >    4002 EXPORT_SYMBOL_GPL(xdp_do_redirect);
> > 
> >   
> > > ---
> > >  include/linux/bpf.h            |  20 ++++
> > >  include/linux/filter.h         |  18 +++-
> > >  include/net/xdp.h              |   1 +
> > >  include/uapi/linux/bpf.h       |  17 +++-
> > >  kernel/bpf/cpumap.c            |   3 +-
> > >  kernel/bpf/devmap.c            | 181 ++++++++++++++++++++++++++++++++-
> > >  net/core/filter.c              |  37 ++++++-
> > >  net/core/xdp.c                 |  29 ++++++
> > >  net/xdp/xskmap.c               |   3 +-
> > >  tools/include/uapi/linux/bpf.h |  17 +++-
> > >  10 files changed, 312 insertions(+), 14 deletions(-)
> > >   
> > [...]
> >   
> > > diff --git a/net/core/filter.c b/net/core/filter.c
> > > index cae56d08a670..05ba5ab4345f 100644
> > > --- a/net/core/filter.c
> > > +++ b/net/core/filter.c
> > > @@ -3926,6 +3926,23 @@ void xdp_do_flush(void)
> > >  }
> > >  EXPORT_SYMBOL_GPL(xdp_do_flush);
> > >  
> > > +void bpf_clear_redirect_map(struct bpf_map *map)
> > > +{
> > > +	struct bpf_redirect_info *ri;
> > > +	int cpu;
> > > +
> > > +	for_each_possible_cpu(cpu) {
> > > +		ri = per_cpu_ptr(&bpf_redirect_info, cpu);
> > > +		/* Avoid polluting remote cacheline due to writes if
> > > +		 * not needed. Once we pass this test, we need the
> > > +		 * cmpxchg() to make sure it hasn't been changed in
> > > +		 * the meantime by remote CPU.
> > > +		 */
> > > +		if (unlikely(READ_ONCE(ri->map) == map))
> > > +			cmpxchg(&ri->map, map, NULL);
> > > +	}
> > > +}
> > > +
> > >  int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
> > >  		    struct bpf_prog *xdp_prog)
> > >  {
> > > @@ -3933,6 +3950,7 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
> > >  	enum bpf_map_type map_type = ri->map_type;
> > >  	void *fwd = ri->tgt_value;
> > >  	u32 map_id = ri->map_id;
> > > +	struct bpf_map *map;
> > >  	int err;
> > >  
> > >  	ri->map_id = 0; /* Valid map id idr range: [1,INT_MAX[ */
> > > @@ -3942,7 +3960,14 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
> > >  	case BPF_MAP_TYPE_DEVMAP:
> > >  		fallthrough;
> > >  	case BPF_MAP_TYPE_DEVMAP_HASH:
> > > -		err = dev_map_enqueue(fwd, xdp, dev);
> > > +		map = READ_ONCE(ri->map);
> > > +		if (map) {
> > > +			WRITE_ONCE(ri->map, NULL);
> > > +			err = dev_map_enqueue_multi(xdp, dev, map,
> > > +						    ri->flags & BPF_F_EXCLUDE_INGRESS);
> > > +		} else {
> > > +			err = dev_map_enqueue(fwd, xdp, dev);
> > > +		}
> > >  		break;
> > >  	case BPF_MAP_TYPE_CPUMAP:
> > >  		err = cpu_map_enqueue(fwd, xdp, dev);
> > > @@ -3984,13 +4009,21 @@ static int xdp_do_generic_redirect_map(struct net_device *dev,
> > >  				       enum bpf_map_type map_type, u32 map_id)
> > >  {
> > >  	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> > > +	struct bpf_map *map;
> > >  	int err;
> > >  
> > >  	switch (map_type) {
> > >  	case BPF_MAP_TYPE_DEVMAP:
> > >  		fallthrough;
> > >  	case BPF_MAP_TYPE_DEVMAP_HASH:
> > > -		err = dev_map_generic_redirect(fwd, skb, xdp_prog);
> > > +		map = READ_ONCE(ri->map);
> > > +		if (map) {
> > > +			WRITE_ONCE(ri->map, NULL);
> > > +			err = dev_map_redirect_multi(dev, skb, xdp_prog, map,
> > > +						     ri->flags & BPF_F_EXCLUDE_INGRESS);
> > > +		} else {
> > > +			err = dev_map_generic_redirect(fwd, skb, xdp_prog);
> > > +		}
> > >  		if (unlikely(err))
> > >  			goto err;
> > >  		break;  
> > 

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer