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BUG: KCSAN: data-race in __rcu_read_unlock / rcu_report_exp_cpu_mult

read to 0xffffffff85a7d440 of 8 bytes by task 9359 on cpu 0:
 rcu_read_unlock_special kernel/rcu/tree_plugin.h:615 [inline]
 __rcu_read_unlock+0x381/0x3c0 kernel/rcu/tree_plugin.h:383
 rcu_read_unlock include/linux/rcupdate.h:652 [inline]
 ip6_route_output_flags+0x84/0x1a0 net/ipv6/route.c:2504
 ip6_dst_lookup_tail+0x25d/0xc30 net/ipv6/ip6_output.c:1049
 ip6_dst_lookup_flow+0x68/0x120 net/ipv6/ip6_output.c:1150
 inet6_csk_route_socket+0x2f7/0x420 net/ipv6/inet6_connection_sock.c:106
 inet6_csk_xmit+0x91/0x1f0 net/ipv6/inet6_connection_sock.c:121
 l2tp_xmit_core net/l2tp/l2tp_core.c:1030 [inline]
 l2tp_xmit_skb+0x8c9/0x8e0 net/l2tp/l2tp_core.c:1132
 pppol2tp_sendmsg+0x2fc/0x3c0 net/l2tp/l2tp_ppp.c:325
 sock_sendmsg_nosec net/socket.c:637 [inline]
 sock_sendmsg+0x9f/0xc0 net/socket.c:657
 ___sys_sendmsg+0x2b7/0x5d0 net/socket.c:2311
 __sys_sendmmsg+0x123/0x350 net/socket.c:2413
 __do_sys_sendmmsg net/socket.c:2442 [inline]
 __se_sys_sendmmsg net/socket.c:2439 [inline]
 __x64_sys_sendmmsg+0x64/0x80 net/socket.c:2439
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffffffff85a7d440 of 8 bytes by task 3504 on cpu 1:
 rcu_report_exp_cpu_mult+0x4f/0xa0 kernel/rcu/tree_exp.h:244
 sync_rcu_exp_select_node_cpus+0x478/0x510 kernel/rcu/tree_exp.h:414
 sync_rcu_exp_select_cpus+0x30c/0x590 kernel/rcu/tree_exp.h:439
 rcu_exp_sel_wait_wake kernel/rcu/tree_exp.h:575 [inline]
 wait_rcu_exp_gp+0x25/0x40 kernel/rcu/tree_exp.h:589
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3504 Comm: kworker/1:2 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: rcu_gp wait_rcu_exp_gp
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