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BUG: KCSAN: data-race in ktime_get_coarse_real_ts64_mg / timekeeping_update_from_shadow

write to 0xffffffff893d74c8 of 304 bytes by interrupt on cpu 0:
 timekeeping_update_from_shadow+0x40d/0x440 kernel/time/timekeeping.c:835
 __timekeeping_advance+0xa68/0xc10 kernel/time/timekeeping.c:2614
 timekeeping_advance kernel/time/timekeeping.c:2622 [inline]
 update_wall_time+0x21/0x50 kernel/time/timekeeping.c:2632
 tick_do_update_jiffies64+0x169/0x1c0 kernel/time/tick-sched.c:149
 tick_sched_do_timer kernel/time/tick-sched.c:253 [inline]
 tick_nohz_handler+0x88/0x380 kernel/time/tick-sched.c:310
 __run_hrtimer kernel/time/hrtimer.c:2032 [inline]
 __hrtimer_run_queues+0x1f8/0x510 kernel/time/hrtimer.c:2096
 hrtimer_interrupt+0x257/0x810 kernel/time/hrtimer.c:2215
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1051 [inline]
 __sysvec_apic_timer_interrupt+0x5f/0x1c0 arch/x86/kernel/apic/apic.c:1068
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0x6f/0x80 arch/x86/kernel/apic/apic.c:1062
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
 kcsan_setup_watchpoint+0x3e8/0x450 kernel/kcsan/core.c:705
 unmap_vmas+0x25b/0x310 mm/memory.c:2180
 exit_mmap+0x1a2/0x5e0 mm/mmap.c:1300
 __mmput+0x28/0x1c0 kernel/fork.c:1187
 mmput+0x40/0x50 kernel/fork.c:1210
 exit_mm+0x113/0x1a0 kernel/exit.c:615
 do_exit+0x438/0x1500 kernel/exit.c:997
 do_group_exit+0x138/0x140 kernel/exit.c:1152
 __do_sys_exit_group kernel/exit.c:1163 [inline]
 __se_sys_exit_group kernel/exit.c:1161 [inline]
 __x64_sys_exit_group+0x1f/0x20 kernel/exit.c:1161
 x64_sys_call+0x3008/0x3020 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff893d7538 of 4 bytes by task 12 on cpu 1:
 tk_xtime_coarse kernel/time/timekeeping.c:217 [inline]
 ktime_get_coarse_real_ts64_mg+0x89/0x1a0 kernel/time/timekeeping.c:2688
 inode_set_ctime_current+0x43/0x8e0 fs/inode.c:2895
 inode_update_cmtime fs/inode.c:2165 [inline]
 inode_update_time+0xec/0x360 fs/inode.c:2223
 generic_update_time fs/inode.c:2254 [inline]
 file_update_time_flags+0x277/0x2e0 fs/inode.c:2487
 file_update_time+0x17/0x20 fs/inode.c:2508
 shmem_file_write_iter+0x9c/0xf0 mm/shmem.c:3421
 lo_rw_aio+0x6a9/0x760 drivers/block/loop.c:-1
 do_req_filebacked drivers/block/loop.c:-1 [inline]
 loop_handle_cmd drivers/block/loop.c:1917 [inline]
 loop_process_work+0x567/0xac0 drivers/block/loop.c:1952
 loop_workfn+0x31/0x40 drivers/block/loop.c:1976
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0x4d4/0x9a0 kernel/workqueue.c:3405
 worker_thread+0x569/0x750 kernel/workqueue.c:3486
 kthread+0x221/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x2b067783 -> 0x2b9f0e03

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 12 Comm: kworker/u8:0 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: loop2 loop_workfn
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