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BUG: KCSAN: data-race in do_tcp_setsockopt / tcp_stream_memory_free

write to 0xffff888092b8e940 of 4 bytes by task 19867 on cpu 0:
 do_tcp_setsockopt+0x678/0x1a70 net/ipv4/tcp.c:3304
 tcp_setsockopt+0x4c/0xa0 net/ipv4/tcp.c:3335
 sock_common_setsockopt+0x5d/0x70 net/core/sock.c:3247
 __sys_setsockopt+0x2dc/0x450 net/socket.c:2132
 __do_sys_setsockopt net/socket.c:2143 [inline]
 __se_sys_setsockopt net/socket.c:2140 [inline]
 __x64_sys_setsockopt+0x62/0x70 net/socket.c:2140
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888092b8e940 of 4 bytes by task 19894 on cpu 1:
 tcp_notsent_lowat include/net/tcp.h:1972 [inline]
 tcp_stream_memory_free+0x45/0xb0 include/net/tcp.h:1985
 __sk_stream_memory_free include/net/sock.h:1274 [inline]
 sk_stream_memory_free include/net/sock.h:1279 [inline]
 sk_stream_wait_memory+0x4bb/0x6e0 net/core/stream.c:145
 tcp_sendmsg_locked+0x8a5/0x2200 net/ipv4/tcp.c:1401
 tcp_sendmsg+0x2c/0x40 net/ipv4/tcp.c:1441
 inet_sendmsg+0x5f/0x80 net/ipv4/af_inet.c:817
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg net/socket.c:671 [inline]
 __sys_sendto+0x2ae/0x380 net/socket.c:1992
 __do_sys_sendto net/socket.c:2004 [inline]
 __se_sys_sendto net/socket.c:2000 [inline]
 __x64_sys_sendto+0x74/0x90 net/socket.c:2000
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19894 Comm: syz-executor.3 Not tainted 5.9.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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