Subject: Re: [PATCH net-next] virito-net: set queues after reset during xdp_set

From: John Fastabend <[email-masked]>
Date: Thu, 16 Feb 2017 20:53:59 -0800

On 17-02-15 01:08 AM, Jason Wang wrote:
> We set queues before reset which will cause a crash[1]. This is
> because is_xdp_raw_buffer_queue() depends on the old xdp queue pairs
> number to do the correct detection. So fix this by:
> 
> - set queues after reset, to keep the old vi->curr_queue_pairs. (in
>   fact setting queues before reset does not works since after feature
>   set, all queue pairs were enabled by default during reset).
> - change xdp_queue_pairs only after virtnet_reset() is succeed.
> 
> [1]

I'm guessing this occurs when enabling XDP while receiving lots of traffic?

> 
> [   74.328168] general protection fault: 0000 [#1] SMP
> [   74.328625] Modules linked in: nfsd xfs libcrc32c virtio_net virtio_pci
> [   74.329117] CPU: 0 PID: 2849 Comm: xdp2 Not tainted 4.10.0-rc7+ #499
> [   74.329577] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.1-0-g8891697-prebuilt.qemu-project.org 04/01/2014
> [   74.330424] task: ffff88007a894000 task.stack: ffffc90004388000
> [   74.330844] RIP: 0010:skb_release_head_state+0x28/0x80
> [   74.331298] RSP: 0018:ffffc9000438b8d0 EFLAGS: 00010206
> [   74.331676] RAX: 0000000000000000 RBX: ffff88007ad96300 RCX: 0000000000000000
> [   74.332217] RDX: ffff88007fc137a8 RSI: ffff88007fc0db28 RDI: 0001bf00000001be
> [   74.332758] RBP: ffffc9000438b8d8 R08: 000000000005008f R09: 00000000000005f9
> [   74.333274] R10: ffff88007d001700 R11: ffffffff820a8a4d R12: ffff88007ad96300
> [   74.333787] R13: 0000000000000002 R14: ffff880036604000 R15: 000077ff80000000
> [   74.334308] FS:  00007fc70d8a7b40(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000
> [   74.334891] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   74.335314] CR2: 00007fff4144a710 CR3: 000000007ab56000 CR4: 00000000003406f0
> [   74.335830] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [   74.336373] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [   74.336895] Call Trace:
> [   74.337086]  skb_release_all+0xd/0x30
> [   74.337356]  consume_skb+0x2c/0x90
> [   74.337607]  free_unused_bufs+0x1ff/0x270 [virtio_net]
> [   74.337988]  ? vp_synchronize_vectors+0x3b/0x60 [virtio_pci]
> [   74.338398]  virtnet_xdp+0x21e/0x440 [virtio_net]
> [   74.338741]  dev_change_xdp_fd+0x101/0x140
> [   74.339048]  do_setlink+0xcf4/0xd20
> [   74.339304]  ? symcmp+0xf/0x20
> [   74.339529]  ? mls_level_isvalid+0x52/0x60
> [   74.339828]  ? mls_range_isvalid+0x43/0x50
> [   74.340135]  ? nla_parse+0xa0/0x100
> [   74.340400]  rtnl_setlink+0xd4/0x120
> [   74.340664]  ? cpumask_next_and+0x30/0x50
> [   74.340966]  rtnetlink_rcv_msg+0x7f/0x1f0
> [   74.341259]  ? sock_has_perm+0x59/0x60
> [   74.341586]  ? napi_consume_skb+0xe2/0x100
> [   74.342010]  ? rtnl_newlink+0x890/0x890
> [   74.342435]  netlink_rcv_skb+0x92/0xb0
> [   74.342846]  rtnetlink_rcv+0x23/0x30
> [   74.343277]  netlink_unicast+0x162/0x210
> [   74.343677]  netlink_sendmsg+0x2db/0x390
> [   74.343968]  sock_sendmsg+0x33/0x40
> [   74.344233]  SYSC_sendto+0xee/0x160
> [   74.344482]  ? SYSC_bind+0xb0/0xe0
> [   74.344806]  ? sock_alloc_file+0x92/0x110
> [   74.345106]  ? fd_install+0x20/0x30
> [   74.345360]  ? sock_map_fd+0x3f/0x60
> [   74.345586]  SyS_sendto+0x9/0x10
> [   74.345790]  entry_SYSCALL_64_fastpath+0x1a/0xa9
> [   74.346086] RIP: 0033:0x7fc70d1b8f6d
> [   74.346312] RSP: 002b:00007fff4144a708 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
> [   74.346785] RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 00007fc70d1b8f6d
> [   74.347244] RDX: 000000000000002c RSI: 00007fff4144a720 RDI: 0000000000000003
> [   74.347683] RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
> [   74.348544] R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff4144bd90
> [   74.349082] R13: 0000000000000002 R14: 0000000000000002 R15: 00007fff4144cda0
> [   74.349607] Code: 00 00 00 55 48 89 e5 53 48 89 fb 48 8b 7f 58 48 85 ff 74 0e 40 f6 c7 01 74 3d 48 c7 43 58 00 00 00 00 48 8b 7b 68 48 85 ff 74 05 <f0> ff 0f 74 20 48 8b 43 60 48 85 c0 74 14 65 8b 15 f3 ab 8d 7e
> [   74.351008] RIP: skb_release_head_state+0x28/0x80 RSP: ffffc9000438b8d0
> [   74.351625] ---[ end trace fe6e19fd11cfc80b ]---
> 
> Fixes: 2de2f7f40ef9 ("virtio_net: XDP support for adjust_head")
> Cc: John Fastabend <[email-masked]>
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/virtio_net.c | 35 ++++++++++++++++++-----------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 11e2853..9ff959c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1775,7 +1775,7 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	struct bpf_prog *old_prog;
> -	u16 oxdp_qp, xdp_qp = 0, curr_qp;
> +	u16 xdp_qp = 0, curr_qp;
>  	int i, err;
>  
>  	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> @@ -1813,24 +1813,24 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  			return PTR_ERR(prog);
>  	}
>  
> -	err = _virtnet_set_queues(vi, curr_qp + xdp_qp);
> -	if (err) {
> -		dev_warn(&dev->dev, "XDP Device queue allocation failure.\n");
> -		goto virtio_queue_err;
> -	}
> -
> -	oxdp_qp = vi->xdp_queue_pairs;
> -
>  	/* Changing the headroom in buffers is a disruptive operation because
>  	 * existing buffers must be flushed and reallocated. This will happen
>  	 * when a xdp program is initially added or xdp is disabled by removing
>  	 * the xdp program resulting in number of XDP queues changing.
>  	 */
>  	if (vi->xdp_queue_pairs != xdp_qp) {
> -		vi->xdp_queue_pairs = xdp_qp;
>  		err = virtnet_reset(vi);
> -		if (err)
> +		if (err) {
> +			dev_warn(&dev->dev, "XDP reset failure.\n");
>  			goto virtio_reset_err;
> +		}
> +		vi->xdp_queue_pairs = xdp_qp;

But xdp_queue_pairs is being used to detect if we should allocate the XDP
headroom. If we move it here do we have a set of buffers in the ring without
the proper headroom when we assign the xdp program below?

> +	}
> +
> +	err = _virtnet_set_queues(vi, curr_qp + xdp_qp);
> +	if (err) {
> +		dev_warn(&dev->dev, "XDP Device queue allocation failure.\n");
> +		goto virtio_queue_err;
>  	}
>  
>  	netif_set_real_num_rx_queues(dev, curr_qp + xdp_qp);
> @@ -1844,17 +1844,18 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>  
>  	return 0;

Thanks,
John