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BUG: KCSAN: data-race in do_nanosleep / prepare_signal

read-write to 0xffff88812127702c of 4 bytes by task 19177 on cpu 1:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 do_nanosleep+0x111/0x3c0 kernel/time/hrtimer.c:1878
 hrtimer_nanosleep kernel/time/hrtimer.c:1931 [inline]
 __do_sys_nanosleep kernel/time/hrtimer.c:1965 [inline]
 __se_sys_nanosleep+0x20b/0x2a0 kernel/time/hrtimer.c:1952
 __x64_sys_nanosleep+0x2d/0x40 kernel/time/hrtimer.c:1952
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812127702c of 4 bytes by interrupt on cpu 0:
 sig_task_ignored kernel/signal.c:94 [inline]
 sig_ignored kernel/signal.c:119 [inline]
 prepare_signal+0x872/0xd80 kernel/signal.c:962
 send_sigqueue+0xe7/0x400 kernel/signal.c:1861
 posix_timer_event kernel/time/posix-timers.c:354 [inline]
 posix_timer_fn+0xdd/0x1f0 kernel/time/posix-timers.c:380
 __run_hrtimer+0x133/0x420 kernel/time/hrtimer.c:1519
 __hrtimer_run_queues kernel/time/hrtimer.c:1583 [inline]
 hrtimer_interrupt+0x36e/0xa10 kernel/time/hrtimer.c:1645
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1085 [inline]
 __sysvec_apic_timer_interrupt+0x6f/0x200 arch/x86/kernel/apic/apic.c:1102
 asm_call_irq_on_stack+0xf/0x20
 __run_sysvec_on_irqstack arch/x86/include/asm/irq_stack.h:37 [inline]
 run_sysvec_on_irqstack_cond arch/x86/include/asm/irq_stack.h:89 [inline]
 sysvec_apic_timer_interrupt+0x52/0x90 arch/x86/kernel/apic/apic.c:1096
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:628
 get_ctx kernel/kcsan/core.c:198 [inline]
 check_access kernel/kcsan/core.c:629 [inline]
 __tsan_read8+0x108/0x180 kernel/kcsan/core.c:842
 ____rb_erase_color lib/rbtree.c:353 [inline]
 rb_erase+0x2fd/0x730 lib/rbtree.c:445
 kernfs_unlink_sibling fs/kernfs/dir.c:398 [inline]
 __kernfs_remove+0x5ad/0x6a0 fs/kernfs/dir.c:1330
 kernfs_remove_by_name_ns+0x47/0x90 fs/kernfs/dir.c:1515
 kernfs_remove_by_name include/linux/kernfs.h:593 [inline]
 remove_files fs/sysfs/group.c:28 [inline]
 sysfs_remove_group+0x99/0x1a0 fs/sysfs/group.c:289
 sysfs_remove_groups+0x3b/0x80 fs/sysfs/group.c:313
 device_remove_groups drivers/base/core.c:2193 [inline]
 device_remove_attrs+0xb9/0xd0 drivers/base/core.c:2390
 device_del+0x3f8/0x8f0 drivers/base/core.c:3269
 netdev_unregister_kobject+0xe1/0xf0 net/core/net-sysfs.c:1864
 rollback_registered_many+0xbd0/0xe40 net/core/dev.c:9522
 unregister_netdevice_many+0x2e/0x1a0 net/core/dev.c:10719
 vti6_exit_batch_net+0x183/0x1b0 net/ipv6/ip6_vti.c:1186
 ops_exit_list net/core/net_namespace.c:190 [inline]
 cleanup_net+0x4cc/0x8e0 net/core/net_namespace.c:604
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 3052 Comm: kworker/u4:4 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
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