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BUG: KCSAN: data-race in rtc_dev_poll / rtc_pie_update_irq

read-write to 0xffff8881031a0b80 of 8 bytes by interrupt on cpu 1:
 rtc_handle_legacy_irq drivers/rtc/interface.c:624 [inline]
 rtc_pie_update_irq+0x93/0xf0 drivers/rtc/interface.c:672
 __run_hrtimer kernel/time/hrtimer.c:1761 [inline]
 __hrtimer_run_queues+0x20c/0x5a0 kernel/time/hrtimer.c:1825
 hrtimer_interrupt+0x21a/0x460 kernel/time/hrtimer.c:1887
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1038 [inline]
 __sysvec_apic_timer_interrupt+0x5c/0x1d0 arch/x86/kernel/apic/apic.c:1055
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
 sysvec_apic_timer_interrupt+0x6f/0x80 arch/x86/kernel/apic/apic.c:1049
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
 strlen+0x20/0x40 lib/string.c:420
 _Z16__fortify_strlenPKcU25pass_dynamic_object_size1 include/linux/fortify-string.h:268 [inline]
 insert_entry fs/proc/proc_sysctl.c:167 [inline]
 insert_header+0x694/0x970 fs/proc/proc_sysctl.c:252
 __register_sysctl_table+0xb69/0xc00 fs/proc/proc_sysctl.c:1396
 register_net_sysctl_sz+0x19e/0x1c0 net/sysctl_net.c:171
 __addrconf_sysctl_register+0x22b/0x330 net/ipv6/addrconf.c:7248
 addrconf_sysctl_register+0xe6/0x130 net/ipv6/addrconf.c:7296
 ipv6_add_dev+0x8da/0xb30 net/ipv6/addrconf.c:458
 addrconf_notify+0x4c8/0x930 net/ipv6/addrconf.c:3654
 notifier_call_chain kernel/notifier.c:85 [inline]
 raw_notifier_call_chain+0x6f/0x1b0 kernel/notifier.c:453
 call_netdevice_notifiers_info+0xae/0x100 net/core/dev.c:2176
 call_netdevice_notifiers_extack net/core/dev.c:2214 [inline]
 call_netdevice_notifiers net/core/dev.c:2228 [inline]
 register_netdevice+0xd48/0xf10 net/core/dev.c:11037
 veth_newlink+0x321/0x770 drivers/net/veth.c:1818
 rtnl_newlink_create+0x1c2/0x630 net/core/rtnetlink.c:3833
 __rtnl_newlink net/core/rtnetlink.c:3950 [inline]
 rtnl_newlink+0xf29/0x12d0 net/core/rtnetlink.c:4065
 rtnetlink_rcv_msg+0x5fb/0x6d0 net/core/rtnetlink.c:6955
 netlink_rcv_skb+0x120/0x220 net/netlink/af_netlink.c:2534
 rtnetlink_rcv+0x1c/0x30 net/core/rtnetlink.c:6982
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x59e/0x670 net/netlink/af_netlink.c:1339
 netlink_sendmsg+0x58b/0x6b0 net/netlink/af_netlink.c:1883
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg+0x142/0x180 net/socket.c:727
 __sys_sendto+0x268/0x330 net/socket.c:2180
 __do_sys_sendto net/socket.c:2187 [inline]
 __se_sys_sendto net/socket.c:2183 [inline]
 __x64_sys_sendto+0x76/0x90 net/socket.c:2183
 x64_sys_call+0x2eb6/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881031a0b80 of 8 bytes by task 16605 on cpu 0:
 rtc_dev_poll+0x78/0xb0 drivers/rtc/dev.c:198
 vfs_poll include/linux/poll.h:82 [inline]
 __io_arm_poll_handler+0x1ee/0xb70 io_uring/poll.c:583
 io_poll_add+0x69/0xe0 io_uring/poll.c:893
 __io_issue_sqe+0xfe/0x2e0 io_uring/io_uring.c:1735
 io_issue_sqe+0x53/0x970 io_uring/io_uring.c:1758
 io_queue_sqe io_uring/io_uring.c:1964 [inline]
 io_req_task_submit+0x6b/0xc0 io_uring/io_uring.c:1363
 io_poll_task_func+0x674/0xa20 io_uring/poll.c:-1
 io_handle_tw_list+0xcc/0x1c0 io_uring/io_uring.c:1050
 tctx_task_work_run+0x6d/0x1a0 io_uring/io_uring.c:1115
 tctx_task_work+0x3f/0x80 io_uring/io_uring.c:1133
 task_work_run+0x12e/0x1a0 kernel/task_work.c:227
 get_signal+0xe13/0xf70 kernel/signal.c:2807
 arch_do_signal_or_restart+0x97/0x480 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x68/0xb0 kernel/entry/common.c:218
 do_syscall_64+0xdd/0x1a0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000000000abc0 -> 0x000000000000acc0

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 16605 Comm: syz.8.2677 Not tainted 6.15.0-rc7-syzkaller-00152-gd0c22de9995b #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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