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BUG: KCSAN: data-race in cgroup_migrate_add_task / do_nanosleep

write to 0xffff888124d67064 of 4 bytes by task 8830 on cpu 0:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 do_nanosleep+0x121/0x3a0 kernel/time/hrtimer.c:1879
 hrtimer_nanosleep kernel/time/hrtimer.c:1932 [inline]
 __do_sys_nanosleep kernel/time/hrtimer.c:1966 [inline]
 __se_sys_nanosleep+0x20b/0x2a0 kernel/time/hrtimer.c:1953
 __x64_sys_nanosleep+0x2d/0x40 kernel/time/hrtimer.c:1953
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888124d67064 of 4 bytes by task 23909 on cpu 1:
 cgroup_migrate_add_task+0x1f/0x2e0 kernel/cgroup/cgroup.c:2299
 cgroup_migrate kernel/cgroup/cgroup.c:2700 [inline]
 cgroup_attach_task+0x16b/0x340 kernel/cgroup/cgroup.c:2740
 cgroup_procs_write+0x151/0x1c0 kernel/cgroup/cgroup.c:4757
 cgroup_file_write+0x15b/0x2d0 kernel/cgroup/cgroup.c:3697
 kernfs_fop_write+0x207/0x2c0 fs/kernfs/file.c:315
 do_loop_readv_writev fs/read_write.c:718 [inline]
 do_iter_write+0x2d2/0x470 fs/read_write.c:1001
 vfs_writev fs/read_write.c:1072 [inline]
 do_writev+0x19a/0x340 fs/read_write.c:1115
 __do_sys_writev fs/read_write.c:1188 [inline]
 __se_sys_writev fs/read_write.c:1185 [inline]
 __x64_sys_writev+0x41/0x50 fs/read_write.c:1185
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 23909 Comm: syz-executor.2 Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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