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BUG: KCSAN: data-race in do_ipv6_setsockopt / ip6_make_skb

write to 0xffff888108b09f6e of 2 bytes by task 17180 on cpu 0:
 do_ipv6_setsockopt+0x775/0x28d0 net/ipv6/ipv6_sockglue.c:813
 ipv6_setsockopt+0x43/0x110 net/ipv6/ipv6_sockglue.c:901
 udpv6_setsockopt+0x76/0x80 net/ipv6/udp.c:1570
 sock_common_setsockopt+0x53/0x60 net/core/sock.c:3262
 __sys_setsockopt+0x27a/0x390 net/socket.c:2127
 __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+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888108b09f6e of 2 bytes by task 17178 on cpu 1:
 ip6_make_skb+0x1e7/0x420 net/ipv6/ip6_output.c:1942
 udpv6_sendmsg+0x14f7/0x1780 net/ipv6/udp.c:1470
 inet6_sendmsg+0x5f/0x80 net/ipv6/af_inet6.c:638
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2352
 ___sys_sendmsg net/socket.c:2406 [inline]
 __sys_sendmmsg+0x322/0x4b0 net/socket.c:2496
 __do_sys_sendmmsg net/socket.c:2525 [inline]
 __se_sys_sendmmsg net/socket.c:2522 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2522
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17178 Comm: syz-executor.3 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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