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BUG: KCSAN: data-race in __ip6_datagram_connect / udpv6_sendmsg

write to 0xffff888107c645c0 of 4 bytes by task 15456 on cpu 1:
 __ipv6_addr_set_half include/net/ipv6.h:561 [inline]
 ipv6_addr_set include/net/ipv6.h:570 [inline]
 ipv6_addr_set_v4mapped include/net/ipv6.h:738 [inline]
 __ip6_datagram_connect+0x19f/0x840 net/ipv6/datagram.c:197
 ip6_datagram_connect+0x2a/0x40 net/ipv6/datagram.c:272
 inet_dgram_connect+0x107/0x190 net/ipv4/af_inet.c:580
 __sys_connect_file net/socket.c:1872 [inline]
 __sys_connect+0x245/0x280 net/socket.c:1889
 __do_sys_connect net/socket.c:1899 [inline]
 __se_sys_connect net/socket.c:1896 [inline]
 __x64_sys_connect+0x3d/0x50 net/socket.c:1896
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888107c645c0 of 4 bytes by task 15470 on cpu 0:
 ipv6_addr_v4mapped include/net/ipv6.h:696 [inline]
 udpv6_sendmsg+0x2c1/0x16b0 net/ipv6/udp.c:1336
 inet6_sendmsg+0x5f/0x80 net/ipv6/af_inet6.c:642
 sock_sendmsg_nosec net/socket.c:702 [inline]
 sock_sendmsg net/socket.c:722 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2385
 ___sys_sendmsg net/socket.c:2439 [inline]
 __sys_sendmmsg+0x315/0x4b0 net/socket.c:2525
 __do_sys_sendmmsg net/socket.c:2554 [inline]
 __se_sys_sendmmsg net/socket.c:2551 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2551
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000 -> 0xffff0000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15470 Comm: syz-executor.0 Not tainted 5.14.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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