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BUG: KCSAN: data-race in batadv_hardif_enable_interface / batadv_send_outstanding_bcast_packet

write to 0xffff88812a3b1470 of 8 bytes by task 7585 on cpu 0:
 batadv_hardif_enable_interface+0x1c3/0x7b0 net/batman-adv/hard-interface.c:754
 batadv_softif_slave_add+0x74/0xe0 net/batman-adv/soft-interface.c:891
 do_set_master net/core/rtnetlink.c:2517 [inline]
 do_setlink+0x86d/0x2220 net/core/rtnetlink.c:2713
 __rtnl_newlink net/core/rtnetlink.c:3374 [inline]
 rtnl_newlink+0xe62/0x1340 net/core/rtnetlink.c:3500
 rtnetlink_rcv_msg+0x71b/0x7b0 net/core/rtnetlink.c:5563
 netlink_rcv_skb+0x13e/0x240 net/netlink/af_netlink.c:2470
 rtnetlink_rcv+0x18/0x20 net/core/rtnetlink.c:5581
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x5e2/0x6b0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x6d8/0x7a0 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg net/socket.c:671 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2353
 ___sys_sendmsg net/socket.c:2407 [inline]
 __sys_sendmsg+0x1df/0x260 net/socket.c:2440
 __do_sys_sendmsg net/socket.c:2449 [inline]
 __se_sys_sendmsg net/socket.c:2447 [inline]
 __x64_sys_sendmsg+0x42/0x50 net/socket.c:2447
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812a3b1470 of 8 bytes by task 21 on cpu 1:
 batadv_send_outstanding_bcast_packet+0x119/0x570 net/batman-adv/send.c:886
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 21 Comm: kworker/u4:1 Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: bat_events batadv_send_outstanding_bcast_packet
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