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BUG: KCSAN: data-race in __thaw_task / futex_wait_queue_me

write to 0xffff8881228020e4 of 4 bytes by task 12922 on cpu 0:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 futex_wait_queue_me+0x1a2/0x290 kernel/futex.c:2627
 futex_wait+0x19b/0x3f0 kernel/futex.c:2733
 do_futex+0xe9/0x18d0 kernel/futex.c:3644
 __do_sys_futex kernel/futex.c:3705 [inline]
 __se_sys_futex kernel/futex.c:3673 [inline]
 __x64_sys_futex+0x2cd/0x3f0 kernel/futex.c:3673
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881228020e4 of 4 bytes by task 12903 on cpu 1:
 frozen include/linux/freezer.h:27 [inline]
 __thaw_task+0x33/0x80 kernel/freezer.c:151
 freezer_attach+0x64/0x180 kernel/cgroup/legacy_freezer.c:179
 cgroup_migrate_execute+0x7b8/0x9b0 kernel/cgroup/cgroup.c:2524
 cgroup_migrate+0xbb/0xf0 kernel/cgroup/cgroup.c:2780
 cgroup_attach_task+0x277/0x400 kernel/cgroup/cgroup.c:2817
 __cgroup1_procs_write.constprop.0+0x203/0x260 kernel/cgroup/cgroup-v1.c:522
 cgroup1_procs_write+0x34/0x50 kernel/cgroup/cgroup-v1.c:535
 cgroup_file_write+0x119/0x320 kernel/cgroup/cgroup.c:3754
 kernfs_fop_write+0x1f4/0x2e0 fs/kernfs/file.c:315
 __vfs_write+0x67/0xc0 fs/read_write.c:494
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12903 Comm: syz-executor.3 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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