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BUG: KCSAN: data-race in virtnet_poll_tx / virtqueue_add

write to 0xffff88821aa38aac of 4 bytes by interrupt on cpu 1:
 virtqueue_add_split drivers/virtio/virtio_ring.c:528 [inline]
 virtqueue_add+0x958/0x1a80 drivers/virtio/virtio_ring.c:1707
 virtqueue_add_outbuf+0x4b/0x70 drivers/virtio/virtio_ring.c:1764
 xmit_skb drivers/net/virtio_net.c:1548 [inline]
 start_xmit+0x5b3/0xbe0 drivers/net/virtio_net.c:1571
 __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
 ip_queue_xmit+0x45/0x60 include/net/ip.h:237

read to 0xffff88821aa38aac of 4 bytes by interrupt on cpu 0:
 virtnet_poll_tx+0x177/0x1d0 drivers/net/virtio_net.c:1498
 napi_poll net/core/dev.c:6392 [inline]
 net_rx_action+0x3ae/0xa90 net/core/dev.c:6460
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 do_IRQ+0xa6/0x180 arch/x86/kernel/irq.c:263
 ret_from_intr+0x0/0x19
 __sanitizer_cov_trace_const_cmp4+0xd/0x20 kernel/kcov.c:188
 ext4_do_update_inode fs/ext4/inode.c:5240 [inline]
 ext4_mark_iloc_dirty+0x29e/0x1580 fs/ext4/inode.c:5876
 ext4_mark_inode_dirty+0xe9/0x420 fs/ext4/inode.c:6055
 ext4_dirty_inode+0x86/0xb0 fs/ext4/inode.c:6086
 __mark_inode_dirty+0x5d4/0x940 fs/fs-writeback.c:2255
 mark_inode_dirty include/linux/fs.h:2165 [inline]
 inode_dec_link_count include/linux/fs.h:2187 [inline]
 d_tmpfile+0x3f/0x140 fs/dcache.c:3116
 ext4_tmpfile+0x1dc/0x310 fs/ext4/namei.c:2660

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 13393 Comm: syz-executor.1 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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