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BUG: KCSAN: data-race in iptunnel_xmit / iptunnel_xmit

read to 0xffff8880b38b9148 of 8 bytes by task 19426 on cpu 0:
 iptunnel_xmit_stats include/net/ip_tunnels.h:455 [inline]
 iptunnel_xmit+0x501/0x520 net/ipv4/ip_tunnel_core.c:83
 ip_tunnel_xmit+0x9aa/0x1400 net/ipv4/ip_tunnel.c:818
 __gre_xmit+0x389/0x4e0 net/ipv4/ip_gre.c:444
 ipgre_xmit+0x332/0x630 net/ipv4/ip_gre.c:628
 __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
 __dev_queue_xmit+0x14c9/0x1b60 net/core/dev.c:3873
 dev_queue_xmit+0x21/0x30 net/core/dev.c:3906
 __bpf_tx_skb net/core/filter.c:2060 [inline]
 __bpf_redirect_common net/core/filter.c:2099 [inline]
 __bpf_redirect+0x4b4/0x710 net/core/filter.c:2106
 ____bpf_clone_redirect net/core/filter.c:2139 [inline]
 bpf_clone_redirect+0x1a5/0x1f0 net/core/filter.c:2111
 0xffffffffa0004523
 bpf_test_run+0x1c3/0x490 net/bpf/test_run.c:44
 bpf_prog_test_run_skb+0x4da/0x840 net/bpf/test_run.c:310
 bpf_prog_test_run kernel/bpf/syscall.c:2108 [inline]
 __do_sys_bpf+0x1664/0x2b90 kernel/bpf/syscall.c:2884
 __se_sys_bpf kernel/bpf/syscall.c:2825 [inline]
 __x64_sys_bpf+0x4c/0x60 kernel/bpf/syscall.c:2825

write to 0xffff8880b38b9148 of 8 bytes by task 19421 on cpu 1:
 iptunnel_xmit_stats include/net/ip_tunnels.h:455 [inline]
 iptunnel_xmit+0x514/0x520 net/ipv4/ip_tunnel_core.c:83
 ip_tunnel_xmit+0x9aa/0x1400 net/ipv4/ip_tunnel.c:818
 __gre_xmit+0x389/0x4e0 net/ipv4/ip_gre.c:444
 ipgre_xmit+0x332/0x630 net/ipv4/ip_gre.c:628
 __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
 __dev_queue_xmit+0x14c9/0x1b60 net/core/dev.c:3873
 dev_queue_xmit+0x21/0x30 net/core/dev.c:3906
 __bpf_tx_skb net/core/filter.c:2060 [inline]
 __bpf_redirect_common net/core/filter.c:2099 [inline]
 __bpf_redirect+0x4b4/0x710 net/core/filter.c:2106
 ____bpf_clone_redirect net/core/filter.c:2139 [inline]
 bpf_clone_redirect+0x1a5/0x1f0 net/core/filter.c:2111
 bpf_prog_bebbfe2050753572+0xf4f/0x1000
 bpf_test_run+0x1c3/0x490 net/bpf/test_run.c:44
 bpf_prog_test_run_skb+0x4da/0x840 net/bpf/test_run.c:310
 bpf_prog_test_run kernel/bpf/syscall.c:2108 [inline]
 __do_sys_bpf+0x1664/0x2b90 kernel/bpf/syscall.c:2884

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19421 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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