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BUG: KCSAN: data-race in rtc_dev_poll / rtc_pie_update_irq

read-write to 0xffff888102776b88 of 8 bytes by interrupt on cpu 1:
 rtc_handle_legacy_irq drivers/rtc/interface.c:651 [inline]
 rtc_pie_update_irq+0x7b/0xd0 drivers/rtc/interface.c:699
 __run_hrtimer kernel/time/hrtimer.c:1777 [inline]
 __hrtimer_run_queues+0x20f/0x590 kernel/time/hrtimer.c:1841
 hrtimer_interrupt+0x21a/0x460 kernel/time/hrtimer.c:1903
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1045 [inline]
 __sysvec_apic_timer_interrupt+0x5f/0x1d0 arch/x86/kernel/apic/apic.c:1062
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0x6f/0x80 arch/x86/kernel/apic/apic.c:1056
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
 kcsan_setup_watchpoint+0x404/0x410 kernel/kcsan/core.c:705
 fib6_clean_node+0x38/0x2a0 net/ipv6/ip6_fib.c:2234
 fib6_walk_continue+0x39f/0x440 net/ipv6/ip6_fib.c:2175
 fib6_walk+0xc5/0x180 net/ipv6/ip6_fib.c:2223
 fib6_clean_tree net/ipv6/ip6_fib.c:2303 [inline]
 __fib6_clean_all net/ipv6/ip6_fib.c:2319 [inline]
 fib6_clean_all+0x107/0x180 net/ipv6/ip6_fib.c:2330
 rt6_sync_down_dev net/ipv6/route.c:5014 [inline]
 rt6_disable_ip+0xb0/0x590 net/ipv6/route.c:5019
 addrconf_ifdown+0x94/0xf90 net/ipv6/addrconf.c:3853
 addrconf_notify+0x222/0x8f0 net/ipv6/addrconf.c:-1
 notifier_call_chain kernel/notifier.c:85 [inline]
 raw_notifier_call_chain+0x6f/0x1b0 kernel/notifier.c:453
 call_netdevice_notifiers_info net/core/dev.c:2243 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2281 [inline]
 call_netdevice_notifiers net/core/dev.c:2295 [inline]
 netif_close_many+0x1df/0x2d0 net/core/dev.c:1798
 unregister_netdevice_many_notify+0x521/0x1710 net/core/dev.c:12366
 rtnl_delete_link net/core/rtnetlink.c:3528 [inline]
 rtnl_dellink+0x433/0x630 net/core/rtnetlink.c:3570
 rtnetlink_rcv_msg+0x64b/0x720 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x123/0x220 net/netlink/af_netlink.c:2550
 rtnetlink_rcv+0x1c/0x30 net/core/rtnetlink.c:6985
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x5c0/0x690 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x5c8/0x6f0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x145/0x170 net/socket.c:742
 ____sys_sendmsg+0x31e/0x4a0 net/socket.c:2592
 ___sys_sendmsg+0x195/0x1e0 net/socket.c:2646
 __sys_sendmsg net/socket.c:2678 [inline]
 __do_sys_sendmsg net/socket.c:2683 [inline]
 __se_sys_sendmsg net/socket.c:2681 [inline]
 __x64_sys_sendmsg+0xd4/0x160 net/socket.c:2681
 x64_sys_call+0x17ba/0x3000 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888102776b88 of 8 bytes by task 3866 on cpu 0:
 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:47 [inline]
 __io_read+0x312/0xc50 io_uring/rw.c:929
 io_read+0x4a/0x190 io_uring/rw.c:1023
 __io_issue_sqe+0xfd/0x2d0 io_uring/io_uring.c:1793
 io_issue_sqe+0x56/0xa70 io_uring/io_uring.c:1816
 io_queue_sqe io_uring/io_uring.c:2043 [inline]
 io_req_task_submit+0x46/0xa0 io_uring/io_uring.c:1435
 io_handle_tw_list+0x1f5/0x230 io_uring/io_uring.c:1122
 tctx_task_work_run+0x42/0x160 io_uring/io_uring.c:1182
 tctx_task_work+0x3f/0x80 io_uring/io_uring.c:1200
 task_work_run+0x130/0x1a0 kernel/task_work.c:233
 get_signal+0xe09/0xf60 kernel/signal.c:2807
 arch_do_signal_or_restart+0x96/0x450 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
 exit_to_user_mode_loop+0x6a/0x6f0 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x1d3/0x2a0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000009dc0 -> 0x0000000000009ec0

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3866 Comm: syz.2.121 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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