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BUG: KCSAN: data-race in virtqueue_get_buf_ctx / vring_interrupt

write to 0xffff88821aaaeac8 of 2 bytes by interrupt on cpu 1:
 virtqueue_get_buf_ctx_split drivers/virtio/virtio_ring.c:721 [inline]
 virtqueue_get_buf_ctx+0x4cc/0x5c0 drivers/virtio/virtio_ring.c:1901
 virtqueue_get_buf+0x29/0x40 drivers/virtio/virtio_ring.c:1907
 free_old_xmit_skbs+0x9e/0x170 drivers/net/virtio_net.c:1359
 start_xmit+0xd3/0xbe0 drivers/net/virtio_net.c:1562
 __netdev_start_xmit include/linux/netdevice.h:4420 [inline]
 netdev_start_xmit include/linux/netdevice.h:4434 [inline]
 xmit_one net/core/dev.c:3280 [inline]
 dev_hard_start_xmit+0xef/0x430 net/core/dev.c:3296
 sch_direct_xmit+0x2b3/0x870 net/sched/sch_generic.c:313
 __dev_xmit_skb net/core/dev.c:3481 [inline]
 __dev_queue_xmit+0x19c6/0x1b60 net/core/dev.c:3842
 dev_queue_xmit+0x21/0x30 net/core/dev.c:3906
 neigh_hh_output include/net/neighbour.h:500 [inline]
 neigh_output include/net/neighbour.h:509 [inline]
 ip_finish_output2+0x83a/0xe40 net/ipv4/ip_output.c:228
 __ip_finish_output net/ipv4/ip_output.c:308 [inline]
 __ip_finish_output+0x23a/0x490 net/ipv4/ip_output.c:290
 ip_finish_output+0x41/0x160 net/ipv4/ip_output.c:318
 NF_HOOK_COND include/linux/netfilter.h:294 [inline]
 ip_output+0xdf/0x210 net/ipv4/ip_output.c:432
 dst_output include/net/dst.h:436 [inline]
 ip_local_out+0x74/0x90 net/ipv4/ip_output.c:125
 __ip_queue_xmit+0x3a8/0xa40 net/ipv4/ip_output.c:532

read to 0xffff88821aaaeac8 of 2 bytes by interrupt on cpu 0:
 more_used drivers/virtio/virtio_ring.c:2030 [inline]
 vring_interrupt+0x36/0x1c0 drivers/virtio/virtio_ring.c:2037
 __handle_irq_event_percpu+0x9a/0x430 kernel/irq/handle.c:149
 handle_irq_event_percpu+0x4b/0xe0 kernel/irq/handle.c:189
 handle_irq_event+0x85/0xca kernel/irq/handle.c:206
 handle_edge_irq+0x1a4/0x4a0 kernel/irq/chip.c:830
 generic_handle_irq_desc include/linux/irqdesc.h:156 [inline]
 do_IRQ+0xa1/0x180 arch/x86/kernel/irq.c:250
 ret_from_intr+0x0/0x19

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7250 Comm: syz-fuzzer Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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