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BUG: KCSAN: data-race in __ip6_make_skb / do_ipv6_setsockopt.isra.0

write to 0xffff8881239704ee of 2 bytes by task 12628 on cpu 0:
 do_ipv6_setsockopt.isra.0+0x1a89/0x2c10 net/ipv6/ipv6_sockglue.c:799
 ipv6_setsockopt+0xd1/0x130 net/ipv6/ipv6_sockglue.c:944
 udpv6_setsockopt+0x71/0xc0 net/ipv6/udp.c:1565
 sock_common_setsockopt+0x67/0x90 net/core/sock.c:3147
 __sys_setsockopt+0x1ce/0x370 net/socket.c:2084
 __do_sys_setsockopt net/socket.c:2100 [inline]
 __se_sys_setsockopt net/socket.c:2097 [inline]
 __x64_sys_setsockopt+0x70/0x90 net/socket.c:2097
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881239704ef of 1 bytes by task 12645 on cpu 1:
 ip6_autoflowlabel net/ipv6/ip6_output.c:183 [inline]
 __ip6_make_skb+0x900/0xf60 net/ipv6/ip6_output.c:1761
 ip6_make_skb+0x211/0x300 net/ipv6/ip6_output.c:1880
 udpv6_sendmsg+0x18b8/0x1c20 net/ipv6/udp.c:1465
 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: 1 PID: 12645 Comm: syz-executor.5 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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