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BUG: KCSAN: data-race in expire_timers / try_to_del_timer_sync

write to 0xffff888237c376c8 of 8 bytes by interrupt on cpu 0:
 expire_timers+0x13d/0x250 kernel/time/timer.c:1463
 __run_timers+0x358/0x420 kernel/time/timer.c:1731
 run_timer_softirq+0x19/0x30 kernel/time/timer.c:1744
 __do_softirq+0x12c/0x26e kernel/softirq.c:558
 invoke_softirq kernel/softirq.c:432 [inline]
 __irq_exit_rcu+0x9a/0xb0 kernel/softirq.c:636
 sysvec_apic_timer_interrupt+0x69/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
 check_access kernel/kcsan/core.c:636 [inline]
 __tsan_read8+0xe9/0x180 kernel/kcsan/core.c:864
 ensure_safe_net_sysctl net/sysctl_net.c:130 [inline]
 register_net_sysctl+0x130/0x190 net/sysctl_net.c:167
 ipv6_sysctl_net_init+0x36a/0x440 net/ipv6/sysctl_net_ipv6.c:266
 ops_init+0x1e7/0x230 net/core/net_namespace.c:140
 setup_net+0x1cb/0x700 net/core/net_namespace.c:333
 copy_net_ns+0x2a9/0x450 net/core/net_namespace.c:474
 create_new_namespaces+0x231/0x560 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0xe2/0x120 kernel/nsproxy.c:226
 ksys_unshare+0x371/0x740 kernel/fork.c:3002
 __do_sys_unshare kernel/fork.c:3076 [inline]
 __se_sys_unshare kernel/fork.c:3074 [inline]
 __x64_sys_unshare+0x1b/0x20 kernel/fork.c:3074
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888237c376c8 of 8 bytes by task 11 on cpu 1:
 try_to_del_timer_sync+0xe3/0x290 kernel/time/timer.c:1231
 del_timer_sync kernel/time/timer.c:1378 [inline]
 schedule_timeout+0x108/0x240 kernel/time/timer.c:1879
 rcu_gp_fqs_loop kernel/rcu/tree.c:1996 [inline]
 rcu_gp_kthread+0xbf7/0xec0 kernel/rcu/tree.c:2169
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

value changed: 0xffffc90000277e60 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11 Comm: rcu_sched Not tainted 5.14.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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