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BUG: KCSAN: data-race in mod_timer / timer_clear_idle

read to 0xffff88812bf1b6e4 of 1 bytes by interrupt on cpu 0:
 forward_timer_base kernel/time/timer.c:892 [inline]
 __mod_timer kernel/time/timer.c:983 [inline]
 mod_timer+0x50d/0x7a0 kernel/time/timer.c:1100
 sk_reset_timer+0x2d/0x70 net/core/sock.c:2838
 tcp_send_delayed_ack+0x21d/0x2b0 net/ipv4/tcp_output.c:3659
 __tcp_ack_snd_check+0x3d1/0x4f0 net/ipv4/tcp_input.c:5246
 tcp_rcv_established+0xce9/0xf50 net/ipv4/tcp_input.c:5672
 tcp_v4_do_rcv+0x381/0x4e0 net/ipv4/tcp_ipv4.c:1561
 tcp_v4_rcv+0x19dc/0x1bb0 net/ipv4/tcp_ipv4.c:1942
 ip_protocol_deliver_rcu+0x4d/0x420 net/ipv4/ip_input.c:204
 ip_local_deliver_finish+0x110/0x140 net/ipv4/ip_input.c:231
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ip_local_deliver+0x133/0x210 net/ipv4/ip_input.c:252
 dst_input include/net/dst.h:442 [inline]
 ip_rcv_finish+0x121/0x160 net/ipv4/ip_input.c:413
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ip_rcv+0x18f/0x1a0 net/ipv4/ip_input.c:523
 __netif_receive_skb_one_core+0xa7/0xe0 net/core/dev.c:5010
 __netif_receive_skb+0x37/0xf0 net/core/dev.c:5124

write to 0xffff88812bf1b6e4 of 1 bytes by task 0 on cpu 1:
 timer_clear_idle+0x42/0x50 kernel/time/timer.c:1675
 tick_nohz_next_event+0x164/0x380 kernel/time/tick-sched.c:708
 __tick_nohz_idle_stop_tick kernel/time/tick-sched.c:943 [inline]
 tick_nohz_idle_stop_tick+0x3c2/0x670 kernel/time/tick-sched.c:973
 cpuidle_idle_call kernel/sched/idle.c:151 [inline]
 do_idle+0x1a5/0x280 kernel/sched/idle.c:263
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
 start_secondary+0x208/0x260 arch/x86/kernel/smpboot.c:264
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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