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

From: Jesper Dangaard Brouer <[email-masked]>
Date: Wed, 16 May 2018 20:53:43 +0200

On Wed, 16 May 2018 17:38:12 +0200
Magnus Karlsson <[email-masked]> wrote:

> On Wed, May 16, 2018 at 4:38 PM, Magnus Karlsson
> <[email-masked]> wrote:
> > On Wed, May 16, 2018 at 4:28 PM, Jesper Dangaard Brouer
> > <[email-masked]> wrote:  
> >> 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                     }  
> >  
> 
> Found it. Checked num_rx_queues in the xsk_bind code instead of
> real_num_rx_queues. The code below will solve the problem. Will post a
> proper patch for it tomorrow. Thanks Jesper for reporting this.
> Appreciated.
> 
> /Magnus
> 
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index ac97902..4b62a1e 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -391,7 +391,8 @@ static int xsk_bind(struct socket *sock, struct
> sockaddr *addr, int addr_len)
>                 goto out_unlock;
>         }
> 
> -       if (sxdp->sxdp_queue_id >= dev->num_rx_queues) {
> +       if ((xs->rx && sxdp->sxdp_queue_id >= dev->real_num_rx_queues) ||
> +           (xs->tx && sxdp->sxdp_queue_id >= dev->real_num_tx_queues)) {
>                 err = -EINVAL;
>                 goto out_unlock;
>         }

Tried this patch... it fixed/catched the problem :-)

$ sudo ./xdpsock --interface=i40e1 --queue=42 --txonly
samples/bpf/xdpsock_user.c:xsk_configure:528: Assertion failed: bind(sfd, (struct sockaddr *)&sxdp, sizeof(sxdp)) == 0: errno: 22/"Invalid argument"
Segmentation fault

You can add:
 Tested-by: Jesper Dangaard Brouer <[email-masked]>

Notice: this bug is not related to this zero-copy patch, but to your
previous patchset, which are in bpf-next.  Thus, you need to send a fix
patch to bpf-next...

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