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BUG: KCSAN: data-race in __ip6_datagram_connect / udpv6_sendmsg

write to 0xffff8880a2c04ab8 of 16 bytes by task 9694 on cpu 1:
 __ip6_datagram_connect+0x521/0x9f0 net/ipv6/datagram.c:238
 ip6_datagram_connect+0x35/0x50 net/ipv6/datagram.c:271
 inet_dgram_connect+0xc5/0x190 net/ipv4/af_inet.c:571
 __sys_connect_file+0xdc/0xf0 net/socket.c:1857
 __sys_connect+0x11b/0x150 net/socket.c:1874
 __do_sys_connect net/socket.c:1885 [inline]
 __se_sys_connect net/socket.c:1882 [inline]
 __x64_sys_connect+0x48/0x60 net/socket.c:1882
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880a2c04ab8 of 8 bytes by task 9708 on cpu 0:
 ipv6_addr_v4mapped include/net/ipv6.h:691 [inline]
 udpv6_sendmsg+0x44d/0x1d40 net/ipv6/udp.c:1273
 inet6_sendmsg+0x69/0x90 net/ipv6/af_inet6.c:576
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0x98/0xc0 net/socket.c:672
 ____sys_sendmsg+0x207/0x4c0 net/socket.c:2343
 ___sys_sendmsg+0xb5/0x100 net/socket.c:2397
 __sys_sendmmsg+0x10e/0x310 net/socket.c:2487
 __do_sys_sendmmsg net/socket.c:2516 [inline]
 __se_sys_sendmmsg net/socket.c:2513 [inline]
 __x64_sys_sendmmsg+0x60/0x80 net/socket.c:2513
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9708 Comm: syz-executor.0 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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