Subject: Re: [RFC PATCH bpf-next 12/12] i40e: implement Tx zero-copy

From: Jesper Dangaard Brouer <[email-masked]>
Date: Wed, 16 May 2018 16:28:40 +0200

On Tue, 15 May 2018 21:06:15 +0200
Björn Töpel <[email-masked]> wrote:

> From: Magnus Karlsson <[email-masked]>
> 
> Here, the zero-copy ndo is implemented. As a shortcut, the existing
> XDP Tx rings are used for zero-copy. This means that and XDP program
> cannot redirect to an AF_XDP enabled XDP Tx ring.

I've changed i40e1 to only have one queue via:
 $ ethtool -L i40e1 combined 1

And then, I'm sending on queue 1, which is/should not be avail... and then crash/BUG:

$ sudo taskset -c 2 ./xdpsock --tx --interface=i40e1 --queue=1

[ 3799.936877] Number of in use tx queues changed invalidating tc mappings. Priority traffic
 classification disabled!
[ 3799.972970] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
[ 3799.980790] PGD 80000007b0992067 P4D 80000007b0992067 PUD 7b62d4067 PMD 0 
[ 3799.987654] Oops: 0002 [#1] PREEMPT SMP PTI
[ 3799.991831] Modules linked in: nf_nat_masquerade_ipv4 tun nfnetlink bridge stp llc nf_nat
 nf_conntrack rpcrdma ib_ipoib rdma_ucm ib_ucm ib_umad rdma_cm ib_cm iw_cm sunrpc mlx5_ib ib
_uverbs ib_core coretemp kvm_intel kvm irqbypass intel_cstate intel_uncore intel_rapl_perf p
cspkr i2c_i801 shpchp wmi ipmi_si ipmi_devintf ipmi_msghandler acpi_pad sch_fq_codel i40e ml
x5_core hid_generic ixgbe igb devlink mdio ptp sd_mod i2c_algo_bit i2c_core pps_core [last u
nloaded: x_tables]
[ 3800.033472] CPU: 2 PID: 2006 Comm: xdpsock Not tainted 4.17.0-rc3-af_xdp03_ZC_rfc+ #155
[ 3800.041465] Hardware name: Supermicro Super Server/X10SRi-F, BIOS 2.0a 08/01/2016
[ 3800.048943] RIP: 0010:i40e_xmit_frame_ring+0xd4/0x1490 [i40e]
[ 3800.054683] RSP: 0018:ffffc9000407bcd0 EFLAGS: 00010293
[ 3800.059900] RAX: 0000000000000000 RBX: ffff88084f0fd200 RCX: 0000000000000000
[ 3800.067022] RDX: 0000000000000000 RSI: 0000000000000006 RDI: ffff8807b6e710c0
[ 3800.074148] RBP: ffff8807c6397800 R08: 00000000000000c0 R09: 0000000000000001
[ 3800.081270] R10: 0000000000000800 R11: 0000000000000010 R12: 0000000000000001
[ 3800.088396] R13: 0000000000000000 R14: 0000000000000001 R15: 000000000000003c
[ 3800.095520] FS:  00007f1d1e00bb80(0000) GS:ffff88087fc80000(0000) knlGS:0000000000000000
[ 3800.103597] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3800.109335] CR2: 0000000000000008 CR3: 000000087d542001 CR4: 00000000003606e0
[ 3800.116458] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 3800.123583] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 3800.130706] Call Trace:
[ 3800.133157]  ? validate_xmit_skb.isra.116+0x1c/0x270
[ 3800.138118]  dev_direct_xmit+0xec/0x1d0
[ 3800.141949]  xsk_sendmsg+0x1f4/0x380
[ 3800.145521]  sock_sendmsg+0x30/0x40
[ 3800.149005]  __sys_sendto+0x10e/0x140
[ 3800.152662]  ? __do_page_fault+0x283/0x500
[ 3800.156751]  __x64_sys_sendto+0x24/0x30
[ 3800.160585]  do_syscall_64+0x42/0xf0
[ 3800.164156]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 3800.169204] RIP: 0033:0x7f1d1d9db430
[ 3800.172774] RSP: 002b:00007fffb7278610 EFLAGS: 00000293 ORIG_RAX: 000000000000002c
[ 3800.180333] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f1d1d9db430
[ 3800.187456] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
[ 3800.194582] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[ 3800.201705] R10: 0000000000000040 R11: 0000000000000293 R12: 0000000000000000
[ 3800.208830] R13: 0000000000000000 R14: 0000000000755510 R15: 00007f1d0d3fc000
[ 3800.215953] Code: d0 0f 86 db 05 00 00 01 c8 0f b7 ca 29 c8 83 e8 01 39 c6 0f 8f ea 06 00 00 48 8b 45 28 48 8d 14 92 41 b9 01 00 00 00 4c 8d 2c d0 <49> 89 5d 08 8b 83 80 00 00 00 66 45 89 4d 14 41 89 45 10 0f b7 
[ 3800.234798] RIP: i40e_xmit_frame_ring+0xd4/0x1490 [i40e] RSP: ffffc9000407bcd0
[ 3800.242005] CR2: 0000000000000008
[ 3800.245320] ---[ end trace f169e36f468e0c59 ]---
[ 3801.726719] Kernel panic - not syncing: Fatal exception in interrupt
[ 3801.733097] Kernel Offset: disabled
[ 3801.785836] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---
[ 3801.793403] ------------[ cut here ]------------

(gdb) list *(i40e_xmit_frame_ring)+0xd4
0x2ccd4 is in i40e_xmit_frame_ring (drivers/net/ethernet/intel/i40e/i40e_txrx.c:4048).
warning: Source file is more recent than executable.
4043			return NETDEV_TX_BUSY;
4044		}
4045	
4046		/* record the location of the first descriptor for this packet */
4047		first = &tx_ring->tx_bi[tx_ring->next_to_use];
4048		first->skb = skb;
4049		first->bytecount = skb->len;
4050		first->gso_segs = 1;
4051	
4052		/* prepare the xmit flags */

(gdb) list *(xsk_sendmsg)+0x1f4
0xffffffff81800c34 is in xsk_sendmsg (net/xdp/xsk.c:251).
warning: Source file is more recent than executable.
246			skb_shinfo(skb)->destructor_arg = (void *)(long)id;
247			skb->destructor = xsk_destruct_skb;
248	
249			err = dev_direct_xmit(skb, xs->queue_id);
250			/* Ignore NET_XMIT_CN as packet might have been sent */
251			if (err == NET_XMIT_DROP || err == NETDEV_TX_BUSY) {
252				err = -EAGAIN;
253				/* SKB consumed by dev_direct_xmit() */
254				goto out;
255			}

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