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BUG: KCSAN: data-race in dst_alloc / percpu_counter_add_batch

read to 0xffff8880b44c2948 of 8 bytes by task 11829 on cpu 1:
 dst_entries_get_fast include/net/dst_ops.h:47 [inline]
 dst_alloc+0x55/0x149 net/core/dst.c:84
 ip6_dst_alloc+0x3d/0x80 net/ipv6/route.c:353
 ip6_rt_cache_alloc+0x8d/0x340 net/ipv6/route.c:1342
 ip6_pol_route+0x4ec/0x5c0 net/ipv6/route.c:2221
 ip6_pol_route_output+0x48/0x60 net/ipv6/route.c:2456
 fib6_rule_lookup+0x95/0x470 net/ipv6/fib6_rules.c:113
 ip6_route_output_flags_noref+0x16b/0x230 net/ipv6/route.c:2488
 ip6_route_output_flags+0x50/0x1a0 net/ipv6/route.c:2501
 ip6_dst_lookup_tail+0x25d/0xc30 net/ipv6/ip6_output.c:1052
 ip6_dst_lookup_flow+0x68/0x120 net/ipv6/ip6_output.c:1153
 rawv6_sendmsg+0x82c/0x21e0 net/ipv6/raw.c:928
 inet_sendmsg+0x6d/0x90 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:637 [inline]
 sock_sendmsg+0x9f/0xc0 net/socket.c:657
 ___sys_sendmsg+0x2b7/0x5d0 net/socket.c:2311
 __sys_sendmmsg+0x123/0x350 net/socket.c:2413
 __do_sys_sendmmsg net/socket.c:2442 [inline]
 __se_sys_sendmmsg net/socket.c:2439 [inline]
 __x64_sys_sendmmsg+0x64/0x80 net/socket.c:2439
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880b44c2948 of 8 bytes by interrupt on cpu 0:
 percpu_counter_add_batch+0xca/0x150 lib/percpu_counter.c:91
 percpu_counter_add include/linux/percpu_counter.h:55 [inline]
 dst_entries_add include/net/dst_ops.h:57 [inline]
 dst_destroy+0x1df/0x210 net/core/dst.c:117
 dst_destroy_rcu+0x1f/0x30 net/core/dst.c:142
 __rcu_reclaim kernel/rcu/rcu.h:222 [inline]
 rcu_do_batch+0x256/0x5b0 kernel/rcu/tree.c:2157
 rcu_core+0x369/0x4d0 kernel/rcu/tree.c:2377
 rcu_core_si+0x12/0x20 kernel/rcu/tree.c:2386
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 arch_local_irq_restore arch/x86/include/asm/paravirt.h:756 [inline]
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
 _raw_spin_unlock_irqrestore+0x51/0x80 kernel/locking/spinlock.c:191
 spin_unlock_irqrestore include/linux/spinlock.h:393 [inline]
 finish_wait+0x65/0x80 kernel/sched/wait.c:365
 pipe_wait+0xcf/0x140 fs/pipe.c:118
 splice_from_pipe_next.part.0+0x6c/0x1d0 fs/splice.c:564
 splice_from_pipe_next fs/splice.c:543 [inline]
 __splice_from_pipe+0xa4/0x480 fs/splice.c:622
 vmsplice_to_user fs/splice.c:1272 [inline]
 do_vmsplice.part.0+0x1c5/0x210 fs/splice.c:1350
 do_vmsplice fs/splice.c:1344 [inline]
 __do_sys_vmsplice+0x15f/0x1c0 fs/splice.c:1371
 __se_sys_vmsplice fs/splice.c:1353 [inline]
 __x64_sys_vmsplice+0x5e/0x80 fs/splice.c:1353
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11826 Comm: syz-executor.4 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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