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BUG: KCSAN: data-race in tcp_poll / tcp_urg

write to 0xffff8880b3cfe744 of 2 bytes by task 25500 on cpu 1:
 tcp_check_urg net/ipv4/tcp_input.c:5360 [inline]
 tcp_urg+0x37c/0x610 net/ipv4/tcp_input.c:5374
 tcp_rcv_established+0x504/0xf50 net/ipv4/tcp_input.c:5704
 tcp_v4_do_rcv+0x3b5/0x520 net/ipv4/tcp_ipv4.c:1564
 sk_backlog_rcv include/net/sock.h:950 [inline]
 __release_sock+0x135/0x1e0 net/core/sock.c:2439
 release_sock+0x61/0x160 net/core/sock.c:2955
 tcp_sendmsg+0x44/0x60 net/ipv4/tcp.c:1437
 inet_sendmsg+0x6d/0x90 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:637 [inline]
 sock_sendmsg+0x9f/0xc0 net/socket.c:657
 __sys_sendto+0x21f/0x320 net/socket.c:1952
 __do_sys_sendto net/socket.c:1964 [inline]
 __se_sys_sendto net/socket.c:1960 [inline]
 __x64_sys_sendto+0x89/0xb0 net/socket.c:1960
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880b3cfe744 of 2 bytes by task 25395 on cpu 0:
 tcp_poll+0x30f/0x800 net/ipv4/tcp.c:576
 sock_poll+0xed/0x250 net/socket.c:1256
 vfs_poll include/linux/poll.h:90 [inline]
 do_select+0x7d0/0x1020 fs/select.c:534
 core_sys_select+0x381/0x550 fs/select.c:677
 do_pselect.constprop.0+0x11d/0x160 fs/select.c:759
 __do_sys_pselect6 fs/select.c:784 [inline]
 __se_sys_pselect6 fs/select.c:769 [inline]
 __x64_sys_pselect6+0x12e/0x170 fs/select.c:769
 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: 25395 Comm: syz-executor.0 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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