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BUG: KCSAN: data-race in event_sched_in / perf_event_update_userpage

write to 0xffff888028b24cd8 of 8 bytes by task 17394 on cpu 0:
 perf_set_shadow_time kernel/events/core.c:2508 [inline]
 event_sched_in+0x63c/0xfd0 kernel/events/core.c:2551
 group_sched_in kernel/events/core.c:2591 [inline]
 merge_sched_in kernel/events/core.c:3670 [inline]
 visit_groups_merge+0xb5f/0x1d40 kernel/events/core.c:3643
 ctx_flexible_sched_in kernel/events/core.c:3711 [inline]
 ctx_sched_in+0x2d4/0x2f0 kernel/events/core.c:3756
 perf_event_sched_in kernel/events/core.c:2695 [inline]
 perf_event_context_sched_in kernel/events/core.c:3800 [inline]
 __perf_event_task_sched_in+0x34d/0x590 kernel/events/core.c:3843
 perf_event_task_sched_in include/linux/perf_event.h:1208 [inline]
 finish_task_switch+0x1ea/0x2a0 kernel/sched/core.c:4194
 context_switch kernel/sched/core.c:4330 [inline]
 __schedule+0x3c1/0x580 kernel/sched/core.c:5078
 preempt_schedule_common kernel/sched/core.c:5238 [inline]
 preempt_schedule+0x54/0x80 kernel/sched/core.c:5263
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:40
 try_to_wake_up+0x298/0x440 kernel/sched/core.c:3474
 wake_up_process kernel/sched/core.c:3538 [inline]
 wake_up_q+0x46/0x80 kernel/sched/core.c:589
 futex_wake+0x375/0x3d0 kernel/futex.c:1623
 do_futex+0x96c/0x20c0 kernel/futex.c:3768
 __do_sys_futex kernel/futex.c:3826 [inline]
 __se_sys_futex+0x2a8/0x390 kernel/futex.c:3792
 __x64_sys_futex+0x74/0x80 kernel/futex.c:3792
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888028b24cd8 of 8 bytes by task 17387 on cpu 1:
 calc_timer_values kernel/events/core.c:5654 [inline]
 perf_event_update_userpage+0x4e/0x300 kernel/events/core.c:5710
 perf_mmap+0xbc9/0xd40 kernel/events/core.c:6197
 call_mmap include/linux/fs.h:1906 [inline]
 mmap_region+0xd5c/0x1450 mm/mmap.c:1807
 do_mmap+0x77d/0xc90 mm/mmap.c:1583
 vm_mmap_pgoff+0xf7/0x1d0 mm/util.c:519
 ksys_mmap_pgoff+0x2a8/0x380 mm/mmap.c:1634
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17387 Comm: syz-executor.0 Not tainted 5.11.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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