netdev - virtio_net: suspicious RCU usage with xdp

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Date:   Wed, 24 Apr 2019 11:13:42 -0600
From:   David Ahern <dsahern@...il.com>
To:     makita.toshiaki@....ntt.co.jp,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: virtio_net: suspicious RCU usage with xdp

seeing an RCU warning testing xdp with virtio net. net-next as of commit
b2f97f7de2f6a4df8e431330cf467576486651c5. No obvious changes so hoping
this rings a bell with someone else.


[  121.990304] =============================
[  121.991488] WARNING: suspicious RCU usage
[  121.992392] 5.1.0-rc5+ #60 Not tainted
[  121.993220] -----------------------------
[  121.994158] /home/dsa/kernel-3.git/drivers/net/virtio_net.c:516
suspicious rcu_dereference_check() usage!
[  121.996284]
               other info that might help us debug this:

[  121.997988]
               rcu_scheduler_active = 2, debug_locks = 1
[  121.999321] no locks held by swapper/1/0.
[  122.000328]
               stack backtrace:
[  122.001253] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.1.0-rc5+ #60
[  122.002474] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.11.1-1 04/01/2014
[  122.004141] Call Trace:
[  122.004651]  <IRQ>
[  122.005082]  dump_stack+0x7e/0xbb
[  122.005757]  lockdep_rcu_suspicious+0x102/0x10b
[  122.006654]  virtnet_xdp_xmit+0x104/0x4fe
[  122.007447]  ? kasan_check_read+0x11/0x13
[  122.008267]  ? mergeable_rx_buffer_size_show+0x163/0x163
[  122.009299]  ? __asan_loadN+0xf/0x11
[  122.010010]  ? pvclock_clocksource_read+0xfa/0x189
[  122.010975]  bq_xmit_all+0xdc/0x358
[  122.011699]  __dev_map_flush+0xc2/0xef
[  122.012472]  xdp_do_flush_map+0x5b/0x74
[  122.013238]  virtnet_poll+0x58f/0x679