virito-net: set queues after reset during xdp_set

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

- passing xdp queue pairs and current queue pairs to virtnet_reset()
- change vi->xdp_qp after reset but before refill, to make sure both
  free_unused_bufs() and refill can make correct detection of XDP.
- remove the duplicated queue pairs setting before virtnet_reset()
  since we will do it inside virtnet_reset()

[1]

[   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 <john.fastabend@gmail.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -1752,7 +1752,7 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 	return err;
 }
 
-static int virtnet_reset(struct virtnet_info *vi)
+static int virtnet_reset(struct virtnet_info *vi, int curr_qp, int xdp_qp)
 {
 	struct virtio_device *dev = vi->vdev;
 	int ret;
@@ -1770,10 +1770,11 @@ static int virtnet_reset(struct virtnet_info *vi)
 	if (ret)
 		goto err;
 
+	vi->xdp_queue_pairs = xdp_qp;
 	ret = virtnet_restore_up(dev);
 	if (ret)
 		goto err;
-	ret = _virtnet_set_queues(vi, vi->curr_queue_pairs);
+	ret = _virtnet_set_queues(vi, curr_qp);
 	if (ret)
 		goto err;
 
@@ -1790,7 +1791,7 @@ 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) ||
@@ -1828,24 +1829,17 @@ 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)
+		err = virtnet_reset(vi, curr_qp + xdp_qp, xdp_qp);
+		if (err) {
+			dev_warn(&dev->dev, "XDP reset failure.\n");
 			goto virtio_reset_err;
+		}
 	}
 
 	netif_set_real_num_rx_queues(dev, curr_qp + xdp_qp);
@@ -1864,12 +1858,6 @@ virtio_reset_err:
 	 * error up to user space for resolution. The underlying reset hung on
 	 * us so not much we can do here.
 	 */
-	dev_warn(&dev->dev, "XDP reset failure and queues unstable\n");
-	vi->xdp_queue_pairs = oxdp_qp;
-virtio_queue_err:
-	/* On queue set error we can unwind bpf ref count and user space can
-	 * retry this is most likely an allocation failure.
-	 */
 	if (prog)
 		bpf_prog_sub(prog, vi->max_queue_pairs - 1);
 	return err;