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

read to 0xffff888128eac620 of 8 bytes by task 18704 on cpu 0:
 sock_sendmsg_nosec net/socket.c:639 [inline]
 sock_sendmsg+0x71/0xc0 net/socket.c:659
 ____sys_sendmsg+0x212/0x4d0 net/socket.c:2330
 ___sys_sendmsg+0xb5/0x100 net/socket.c:2384
 __sys_sendmmsg+0x123/0x350 net/socket.c:2474
 __do_sys_sendmmsg net/socket.c:2503 [inline]
 __se_sys_sendmmsg net/socket.c:2500 [inline]
 __x64_sys_sendmmsg+0x64/0x80 net/socket.c:2500
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888128eac620 of 8 bytes by task 18708 on cpu 1:
 do_ipv6_setsockopt.isra.0+0xfdf/0x2cf0 net/ipv6/ipv6_sockglue.c:231
 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:3149
 __sys_setsockopt+0x1ce/0x370 net/socket.c:2117
 __do_sys_setsockopt net/socket.c:2133 [inline]
 __se_sys_setsockopt net/socket.c:2130 [inline]
 __x64_sys_setsockopt+0x70/0x90 net/socket.c:2130
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18708 Comm: syz-executor.0 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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