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BUG: KCSAN: data-race in ip6_dst_gc / ip6_dst_gc

read to 0xffff888120850a8c of 4 bytes by task 11261 on cpu 0:
 dst_entries_get_fast include/net/dst_ops.h:47 [inline]
 ip6_dst_gc+0xf6/0x220 net/ipv6/route.c:3168
 dst_alloc+0x104/0x149 net/core/dst.c:85
 ip6_dst_alloc+0x3d/0x80 net/ipv6/route.c:353
 ip6_rt_cache_alloc+0x12b/0x480 net/ipv6/route.c:1342
 ip6_pol_route+0x5d2/0x730 net/ipv6/route.c:2221
 ip6_pol_route_output+0x48/0x60 net/ipv6/route.c:2453
 fib6_rule_lookup+0x3d6/0x470 net/ipv6/fib6_rules.c:118
 ip6_route_output_flags_noref+0x16b/0x230 net/ipv6/route.c:2485
 ip6_route_output_flags+0x50/0x1a0 net/ipv6/route.c:2498
 ip6_dst_lookup_tail+0x25d/0xc50 net/ipv6/ip6_output.c:1052
 ip6_dst_lookup_flow+0x5c/0x110 net/ipv6/ip6_output.c:1153
 rawv6_sendmsg+0x9be/0x2340 net/ipv6/raw.c:928
 inet_sendmsg+0x6d/0x90 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:639 [inline]
 sock_sendmsg+0x9f/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 0xffff888120850a8c of 4 bytes by task 11260 on cpu 1:
 ip6_dst_gc+0x19f/0x220 net/ipv6/route.c:3179
 dst_alloc+0x104/0x149 net/core/dst.c:85
 ip6_dst_alloc+0x3d/0x80 net/ipv6/route.c:353
 ip6_rt_cache_alloc+0x12b/0x480 net/ipv6/route.c:1342
 ip6_pol_route+0x5d2/0x730 net/ipv6/route.c:2221
 ip6_pol_route_output+0x48/0x60 net/ipv6/route.c:2453
 fib6_rule_lookup+0x3d6/0x470 net/ipv6/fib6_rules.c:118
 ip6_route_output_flags_noref+0x16b/0x230 net/ipv6/route.c:2485
 ip6_route_output_flags+0x50/0x1a0 net/ipv6/route.c:2498
 ip6_dst_lookup_tail+0x25d/0xc50 net/ipv6/ip6_output.c:1052
 ip6_dst_lookup_flow+0x5c/0x110 net/ipv6/ip6_output.c:1153
 rawv6_sendmsg+0x9be/0x2340 net/ipv6/raw.c:928
 inet_sendmsg+0x6d/0x90 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:639 [inline]
 sock_sendmsg+0x9f/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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11260 Comm: syz-executor.2 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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