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BUG: KCSAN: data-race in detach_buf_split / virtnet_poll

write to 0xffff88812969adac of 4 bytes by interrupt on cpu 0:
 detach_buf_split+0x12a/0x3d0 drivers/virtio/virtio_ring.c:635
 virtqueue_get_buf_ctx_split drivers/virtio/virtio_ring.c:720 [inline]
 virtqueue_get_buf_ctx+0x4b4/0x5c0 drivers/virtio/virtio_ring.c:1900
 virtqueue_get_buf+0x29/0x40 drivers/virtio/virtio_ring.c:1906
 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:4510 [inline]
 netdev_start_xmit include/linux/netdevice.h:4524 [inline]
 xmit_one net/core/dev.c:3470 [inline]
 dev_hard_start_xmit+0xef/0x430 net/core/dev.c:3486
 sch_direct_xmit+0x2b3/0x900 net/sched/sch_generic.c:313
 __dev_xmit_skb net/core/dev.c:3671 [inline]
 __dev_queue_xmit+0x13e2/0x1ba0 net/core/dev.c:4032
 dev_queue_xmit+0x21/0x30 net/core/dev.c:4096
 neigh_hh_output include/net/neighbour.h:499 [inline]
 neigh_output include/net/neighbour.h:508 [inline]
 ip_finish_output2+0x89b/0xea0 net/ipv4/ip_output.c:228
 __ip_finish_output net/ipv4/ip_output.c:306 [inline]
 __ip_finish_output+0x23a/0x4b0 net/ipv4/ip_output.c:288
 ip_finish_output+0x41/0x160 net/ipv4/ip_output.c:316
 NF_HOOK_COND include/linux/netfilter.h:296 [inline]
 ip_output+0xfe/0x230 net/ipv4/ip_output.c:430
 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:530
 ip_queue_xmit+0x45/0x60 include/net/ip.h:237
 __tcp_transmit_skb+0xea3/0x1df0 net/ipv4/tcp_output.c:1234
 __tcp_send_ack+0x246/0x300 net/ipv4/tcp_output.c:3771
 tcp_send_ack+0x34/0x40 net/ipv4/tcp_output.c:3777
 __tcp_ack_snd_check+0xd9/0x580 net/ipv4/tcp_input.c:5263
 tcp_ack_snd_check net/ipv4/tcp_input.c:5309 [inline]
 tcp_rcv_established+0x750/0xf50 net/ipv4/tcp_input.c:5730
 tcp_v4_do_rcv+0x3b5/0x520 net/ipv4/tcp_ipv4.c:1619
 tcp_v4_rcv+0x1c30/0x1e20 net/ipv4/tcp_ipv4.c:2001
 ip_protocol_deliver_rcu+0x4d/0x420 net/ipv4/ip_input.c:204
 ip_local_deliver_finish+0x110/0x140 net/ipv4/ip_input.c:231
 NF_HOOK include/linux/netfilter.h:307 [inline]
 NF_HOOK include/linux/netfilter.h:301 [inline]
 ip_local_deliver+0x133/0x210 net/ipv4/ip_input.c:252
 dst_input include/net/dst.h:442 [inline]
 ip_sublist_rcv_finish+0xf8/0x140 net/ipv4/ip_input.c:549
 ip_list_rcv_finish net/ipv4/ip_input.c:599 [inline]
 ip_sublist_rcv+0x418/0x550 net/ipv4/ip_input.c:607
 ip_list_rcv+0x2f5/0x322 net/ipv4/ip_input.c:642
 __netif_receive_skb_list_ptype net/core/dev.c:5241 [inline]
 __netif_receive_skb_list_ptype net/core/dev.c:5230 [inline]
 __netif_receive_skb_list_core+0x350/0x5c0 net/core/dev.c:5289
 __netif_receive_skb_list net/core/dev.c:5341 [inline]
 netif_receive_skb_list_internal+0x5d8/0x830 net/core/dev.c:5436
 gro_normal_list.part.0+0x3a/0xb0 net/core/dev.c:5547
 gro_normal_list net/core/dev.c:6280 [inline]
 napi_complete_done+0x1df/0x3c0 net/core/dev.c:6268
 virtqueue_napi_complete+0x3a/0xa0 drivers/net/virtio_net.c:329
 virtnet_poll+0x7a6/0x7d0 drivers/net/virtio_net.c:1432
 napi_poll net/core/dev.c:6582 [inline]
 net_rx_action+0x3ae/0xa90 net/core/dev.c:6650
 __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:546 [inline]
 do_IRQ+0x81/0x130 arch/x86/kernel/irq.c:263
 ret_from_intr+0x0/0x21
 __read_once_size include/linux/compiler.h:232 [inline]
 arch_atomic64_read arch/x86/include/asm/atomic64_64.h:22 [inline]
 atomic64_read include/asm-generic/atomic-instrumented.h:838 [inline]
 atomic_long_read include/asm-generic/atomic-long.h:29 [inline]
 find_watchpoint kernel/kcsan/core.c:117 [inline]
 check_access kernel/kcsan/core.c:537 [inline]
 __tsan_read8+0x34/0x100 kernel/kcsan/core.c:686
 ext4_htree_store_dirent+0x11f/0x2a0 fs/ext4/dir.c:474
 htree_dirblock_to_tree+0x22a/0x560 fs/ext4/namei.c:1045
 ext4_htree_fill_tree+0x179/0x6b0 fs/ext4/namei.c:1120
 ext4_dx_readdir fs/ext4/dir.c:579 [inline]
 ext4_readdir+0x508/0x1e20 fs/ext4/dir.c:128
 iterate_dir+0x312/0x380 fs/readdir.c:65
 __do_sys_getdents fs/readdir.c:285 [inline]
 __se_sys_getdents fs/readdir.c:267 [inline]
 __x64_sys_getdents+0x14b/0x2b0 fs/readdir.c:267
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812969adac of 4 bytes by interrupt on cpu 1:
 virtnet_poll_cleantx drivers/net/virtio_net.c:1413 [inline]
 virtnet_poll+0x22d/0x7d0 drivers/net/virtio_net.c:1426
 napi_poll net/core/dev.c:6582 [inline]
 net_rx_action+0x3ae/0xa90 net/core/dev.c:6650
 __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:546 [inline]
 do_IRQ+0x81/0x130 arch/x86/kernel/irq.c:263
 ret_from_intr+0x0/0x21

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7986 Comm: sshd Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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