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BUG: KCSAN: data-race in ipv6_setsockopt / kernel_sendpage

write to 0xffff888104a45060 of 8 bytes by task 12874 on cpu 0:
 do_ipv6_setsockopt net/ipv6/ipv6_sockglue.c:493 [inline]
 ipv6_setsockopt+0x3399/0x34f0 net/ipv6/ipv6_sockglue.c:1012
 udpv6_setsockopt+0x85/0x90 net/ipv6/udp.c:1647
 sock_common_setsockopt+0x5d/0x70 net/core/sock.c:3478
 __sys_setsockopt+0x18f/0x200 net/socket.c:2176
 __do_sys_setsockopt net/socket.c:2187 [inline]
 __se_sys_setsockopt net/socket.c:2184 [inline]
 __x64_sys_setsockopt+0x62/0x70 net/socket.c:2184
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888104a45060 of 8 bytes by task 12875 on cpu 1:
 kernel_sendpage+0x30/0x200 net/socket.c:3501
 sock_sendpage+0x5a/0x70 net/socket.c:1003
 pipe_to_sendpage+0x128/0x160 fs/splice.c:364
 splice_from_pipe_feed fs/splice.c:418 [inline]
 __splice_from_pipe+0x207/0x500 fs/splice.c:562
 splice_from_pipe fs/splice.c:597 [inline]
 generic_splice_sendpage+0x94/0xd0 fs/splice.c:746
 do_splice_from fs/splice.c:767 [inline]
 do_splice+0xa0e/0xde0 fs/splice.c:1079
 __do_splice fs/splice.c:1144 [inline]
 __do_sys_splice fs/splice.c:1350 [inline]
 __se_sys_splice+0x2bd/0x3a0 fs/splice.c:1332
 __x64_sys_splice+0x74/0x80 fs/splice.c:1332
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0xffffffff83160af0 -> 0xffffffff8315b1d0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12875 Comm: syz-executor.2 Not tainted 5.15.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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