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

On Fri, Feb 17, 2017 at 03:30:51PM -0800, John Fastabend wrote:

On 17-02-16 09:10 PM, Jason Wang wrote:

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On 2017年02月17日 12:53, John Fastabend wrote:

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On 17-02-15 01:08 AM, Jason Wang wrote:

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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?

I hit this then disabling XDP while receiving lots of traffic.

[...]

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+        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?

Right, so how about passing xdp_queue_pairs as a parameter to virtnet_reset().
Then virtnet_reset() can set it after _remove_vq_common() but before
virtnet_restore_up()?

Thanks

Sounds like a reasonable fix to me.

I'm fine with that.

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+    }
+
+    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

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