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BUG: KCSAN: data-race in sock_gettstamp / udpv6_recvmsg

write to 0xffff8880799bc060 of 8 bytes by task 22785 on cpu 0:
 instrument_write include/linux/instrumented.h:42 [inline]
 __set_bit include/asm-generic/bitops/instrumented-non-atomic.h:27 [inline]
 sock_set_flag include/net/sock.h:876 [inline]
 sock_enable_timestamp net/core/sock.c:3160 [inline]
 sock_gettstamp+0x6d/0x1e0 net/core/sock.c:3122
 sock_ioctl+0x3c5/0x5b0 net/socket.c:1194
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880799bc060 of 8 bytes by task 22778 on cpu 1:
 sock_recv_ts_and_drops include/net/sock.h:2455 [inline]
 udpv6_recvmsg+0x68b/0xc50 net/ipv6/udp.c:392
 inet6_recvmsg+0xa3/0x210 net/ipv6/af_inet6.c:654
 ____sys_recvmsg+0x15a/0x2e0 include/linux/uio.h:234
 ___sys_recvmsg net/socket.c:2618 [inline]
 do_recvmmsg+0x35c/0xa30 net/socket.c:2716
 __sys_recvmmsg net/socket.c:2795 [inline]
 __do_sys_recvmmsg net/socket.c:2818 [inline]
 __se_sys_recvmmsg net/socket.c:2811 [inline]
 __x64_sys_recvmmsg+0xcc/0x150 net/socket.c:2811
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 22778 Comm: syz-executor.1 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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