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BUG: KCSAN: data-race in l2tp_tunnel_del_work / sk_common_release

write to 0xffff88810e001278 of 8 bytes by task 22775 on cpu 1:
 sk_set_socket include/net/sock.h:1868 [inline]
 sock_orphan include/net/sock.h:1887 [inline]
 sk_common_release+0x99/0x210 net/core/sock.c:3280
 udp_lib_close+0x11/0x20 include/net/udp.h:209
 inet_release+0xed/0x130 net/ipv4/af_inet.c:431
 inet6_release+0x3a/0x50 net/ipv6/af_inet6.c:475
 __sock_release net/socket.c:597 [inline]
 sock_close+0x6c/0x150 net/socket.c:1256
 __fput+0x24b/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0x8e/0x110 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x16b/0x1a0 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810e001278 of 8 bytes by task 8 on cpu 0:
 l2tp_tunnel_del_work+0x3a/0x380 net/l2tp/l2tp_core.c:1231
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8 Comm: kworker/u4:0 Not tainted 5.11.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: l2tp l2tp_tunnel_del_work
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