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BUG: KCSAN: data-race in rfcomm_sock_sendmsg / rfcomm_sock_shutdown

write to 0xffff88809c65b66a of 1 bytes by task 9578 on cpu 1:
 rfcomm_sock_shutdown+0x9b/0x150 net/bluetooth/rfcomm/sock.c:924
 __sys_shutdown+0xa2/0x130 net/socket.c:2160
 __do_sys_shutdown net/socket.c:2168 [inline]
 __se_sys_shutdown net/socket.c:2166 [inline]
 __x64_sys_shutdown+0x3a/0x50 net/socket.c:2166
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88809c65b66a of 1 bytes by task 9576 on cpu 0:
 rfcomm_sock_sendmsg+0xc6/0x380 net/bluetooth/rfcomm/sock.c:573
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9576 Comm: syz-executor.5 Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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