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BUG: KCSAN: data-race in inet_putpeer / inet_putpeer

write to 0xffff8880b2b87690 of 4 bytes by interrupt on cpu 0:
 inet_putpeer+0x37/0xa0 net/ipv4/inetpeer.c:240
 ip4_frag_free+0x3d/0x50 net/ipv4/ip_fragment.c:102
 inet_frag_destroy_rcu+0x58/0x80 net/ipv4/inet_fragment.c:228
 __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
 run_ksoftirqd+0x46/0x60 kernel/softirq.c:603
 smpboot_thread_fn+0x37d/0x4a0 kernel/smpboot.c:165
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

write to 0xffff8880b2b87690 of 4 bytes by interrupt on cpu 1:
 inet_putpeer+0x37/0xa0 net/ipv4/inetpeer.c:240
 ip4_frag_free+0x3d/0x50 net/ipv4/ip_fragment.c:102
 inet_frag_destroy_rcu+0x58/0x80 net/ipv4/inet_fragment.c:228
 __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
 __read_once_size include/linux/compiler.h:227 [inline]
 check_kcov_mode kernel/kcov.c:70 [inline]
 __sanitizer_cov_trace_pc+0x26/0x50 kernel/kcov.c:102
 rcu_read_lock include/linux/rcupdate.h:597 [inline]
 inet_twsk_purge+0x69/0x2d0 net/ipv4/inet_timewait_sock.c:268
 dccp_v6_exit_batch+0x23/0x30 net/dccp/ipv6.c:1114
 ops_exit_list.isra.0+0xa2/0xc0 net/core/net_namespace.c:175
 setup_net+0x319/0x4b0 net/core/net_namespace.c:358
 copy_net_ns+0x1e3/0x390 net/core/net_namespace.c:476
 create_new_namespaces+0x2e2/0x4b0 kernel/nsproxy.c:103
 unshare_nsproxy_namespaces+0xb9/0x170 kernel/nsproxy.c:202
 ksys_unshare+0x2dc/0x710 kernel/fork.c:2827
 __do_sys_unshare kernel/fork.c:2895 [inline]
 __se_sys_unshare kernel/fork.c:2893 [inline]
 __x64_sys_unshare+0x28/0x40 kernel/fork.c:2893
 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: 1 PID: 10893 Comm: syz-executor.3 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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