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BUG: KCSAN: data-race in ip6_dst_gc / ip6_dst_gc

read-write to 0xffff88813784498c of 4 bytes by task 9264 on cpu 1:
 ip6_dst_gc+0x1dd/0x210 net/ipv6/route.c:3218
 dst_alloc+0xa2/0x2c0 net/core/dst.c:87
 ip6_dst_alloc net/ipv6/route.c:356 [inline]
 ip6_rt_cache_alloc+0x210/0x5c0 net/ipv6/route.c:1346
 ip6_pol_route+0xbe8/0xd60 net/ipv6/route.c:2246
 ip6_pol_route_output+0x3b/0x50 net/ipv6/route.c:2478
 pol_lookup_func include/net/ip6_fib.h:583 [inline]
 fib6_rule_lookup+0xef/0x320 net/ipv6/fib6_rules.c:115
 ip6_route_output_flags_noref+0x1e3/0x200 net/ipv6/route.c:2510
 ip6_route_output_flags+0x2f/0x150 net/ipv6/route.c:2523
 ip6_dst_lookup_tail+0xf0/0x9b0 net/ipv6/ip6_output.c:1090
 ip6_dst_lookup_flow+0x44/0xc0 net/ipv6/ip6_output.c:1193
 rawv6_sendmsg+0xbc2/0x1320 net/ipv6/raw.c:928
 inet_sendmsg+0x5f/0x80 net/ipv4/af_inet.c:817
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x352/0x4c0 net/socket.c:2345
 ___sys_sendmsg net/socket.c:2399 [inline]
 __sys_sendmmsg+0x335/0x4b0 net/socket.c:2489
 __do_sys_sendmmsg net/socket.c:2518 [inline]
 __se_sys_sendmmsg net/socket.c:2515 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2515
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read-write to 0xffff88813784498c of 4 bytes by task 9269 on cpu 0:
 ip6_dst_gc+0x1dd/0x210 net/ipv6/route.c:3218
 dst_alloc+0xa2/0x2c0 net/core/dst.c:87
 ip6_dst_alloc net/ipv6/route.c:356 [inline]
 ip6_rt_cache_alloc+0x210/0x5c0 net/ipv6/route.c:1346
 ip6_pol_route+0xbe8/0xd60 net/ipv6/route.c:2246
 ip6_pol_route_output+0x3b/0x50 net/ipv6/route.c:2478
 pol_lookup_func include/net/ip6_fib.h:583 [inline]
 fib6_rule_lookup+0xef/0x320 net/ipv6/fib6_rules.c:115
 ip6_route_output_flags_noref+0x1e3/0x200 net/ipv6/route.c:2510
 ip6_route_output_flags+0x2f/0x150 net/ipv6/route.c:2523
 ip6_dst_lookup_tail+0xf0/0x9b0 net/ipv6/ip6_output.c:1090
 ip6_dst_lookup_flow+0x44/0xc0 net/ipv6/ip6_output.c:1193
 rawv6_sendmsg+0xbc2/0x1320 net/ipv6/raw.c:928
 inet_sendmsg+0x5f/0x80 net/ipv4/af_inet.c:817
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x352/0x4c0 net/socket.c:2345
 ___sys_sendmsg net/socket.c:2399 [inline]
 __sys_sendmmsg+0x335/0x4b0 net/socket.c:2489
 __do_sys_sendmmsg net/socket.c:2518 [inline]
 __se_sys_sendmmsg net/socket.c:2515 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2515
 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: 0 PID: 9269 Comm: syz-executor.2 Not tainted 5.11.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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