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BUG: KCSAN: data-race in rtc_dev_poll / rtc_pie_update_irq

read-write to 0xffff88810354fb88 of 8 bytes by interrupt on cpu 0:
 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+0x20f/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:1039 [inline]
 __sysvec_apic_timer_interrupt+0x5c/0x1d0 arch/x86/kernel/apic/apic.c:1056
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
 sysvec_apic_timer_interrupt+0x6f/0x80 arch/x86/kernel/apic/apic.c:1050
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
 kcsan_setup_watchpoint+0x415/0x430 kernel/kcsan/core.c:705
 strlen+0x19/0x40 lib/string.c:420
 __fortify_strlen 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:1399
 register_net_sysctl_sz+0x19e/0x1c0 net/sysctl_net.c:171
 __devinet_sysctl_register+0x1cd/0x260 net/ipv4/devinet.c:2678
 devinet_sysctl_register+0x101/0x150 net/ipv4/devinet.c:2718
 inetdev_init+0x1fb/0x370 net/ipv4/devinet.c:291
 inetdev_event+0x423/0xc10 net/ipv4/devinet.c:1591
 notifier_call_chain kernel/notifier.c:85 [inline]
 raw_notifier_call_chain+0x6c/0x1b0 kernel/notifier.c:453
 call_netdevice_notifiers_info+0xae/0x100 net/core/dev.c:2229
 call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
 call_netdevice_notifiers net/core/dev.c:2281 [inline]
 register_netdevice+0xd48/0xf00 net/core/dev.c:11244
 tun_set_iff+0x5f1/0x890 drivers/net/tun.c:2804
 __tun_chr_ioctl+0x5f0/0x14c0 drivers/net/tun.c:3085
 tun_chr_ioctl+0x27/0x40 drivers/net/tun.c:3334
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:584
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:584
 x64_sys_call+0x1816/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810354fb88 of 8 bytes by task 9025 on cpu 1:
 rtc_dev_poll+0x78/0xb0 drivers/rtc/dev.c:198
 vfs_poll include/linux/poll.h:82 [inline]
 io_file_supports_nowait io_uring/rw.c:46 [inline]
 __io_read+0x2e4/0xc20 io_uring/rw.c:927
 io_read+0x1c/0x60 io_uring/rw.c:1020
 __io_issue_sqe+0xfe/0x2e0 io_uring/io_uring.c:1773
 io_issue_sqe+0x53/0x970 io_uring/io_uring.c:1796
 io_queue_sqe io_uring/io_uring.c:2025 [inline]
 io_req_task_submit+0x6b/0xd0 io_uring/io_uring.c:1415
 io_handle_tw_list+0x190/0x1c0 io_uring/io_uring.c:1102
 tctx_task_work_run+0x6d/0x1a0 io_uring/io_uring.c:1167
 tctx_task_work+0x3f/0x80 io_uring/io_uring.c:1185
 task_work_run+0x131/0x1a0 kernel/task_work.c:227
 get_signal+0xe13/0xf70 kernel/signal.c:2807
 arch_do_signal_or_restart+0x96/0x480 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x7a/0x100 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000027c0 -> 0x00000000000028c0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 9025 Comm: syz.8.2279 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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