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BUG: KCSAN: data-race in __ip6_datagram_connect / udpv6_sendmsg

write to 0xffff88810d40c580 of 4 bytes by task 24461 on cpu 1:
 __ipv6_addr_set_half include/net/ipv6.h:560 [inline]
 ipv6_addr_set include/net/ipv6.h:569 [inline]
 ipv6_addr_set_v4mapped include/net/ipv6.h:732 [inline]
 __ip6_datagram_connect+0x66a/0x9f0 net/ipv6/datagram.c:196
 ip6_datagram_connect+0x39/0x60 net/ipv6/datagram.c:271
 inet_dgram_connect+0xcf/0x1a0 net/ipv4/af_inet.c:571
 __sys_connect+0x1e9/0x250 net/socket.c:1828
 __do_sys_connect net/socket.c:1839 [inline]
 __se_sys_connect net/socket.c:1836 [inline]
 __x64_sys_connect+0x4c/0x60 net/socket.c:1836
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810d40c580 of 4 bytes by task 24463 on cpu 0:
 ipv6_addr_v4mapped include/net/ipv6.h:695 [inline]
 udpv6_sendmsg+0x456/0x1c20 net/ipv6/udp.c:1274
 inet6_sendmsg+0x6d/0x90 net/ipv6/af_inet6.c:576
 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: 24463 Comm: syz-executor.0 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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