syzbot

==================================================================
BUG: KCSAN: data-race in cgroup_finalize_control / get_mem_cgroup_from_page

write to 0xffff88821b67307c of 4 bytes by task 3370 on cpu 1:
 css_clear_dir kernel/cgroup/cgroup.c:1648 [inline]
 cgroup_apply_control_disable kernel/cgroup/cgroup.c:3110 [inline]
 cgroup_finalize_control+0x7b3/0xb90 kernel/cgroup/cgroup.c:3171
 rebind_subsystems+0x314/0x730 kernel/cgroup/cgroup.c:1743
 cgroup_destroy_root+0x7e/0x410 kernel/cgroup/cgroup.c:1320
 css_free_rwork_fn+0x251/0x390 kernel/cgroup/cgroup.c:4972
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

read to 0xffff88821b67307c of 4 bytes by task 10815 on cpu 0:
 css_tryget include/linux/cgroup.h:353 [inline]
 get_mem_cgroup_from_page+0x2d/0xb0 mm/memcontrol.c:959
 alloc_page_buffers+0x2a/0x2c0 fs/buffer.c:851
 create_empty_buffers+0x2c/0x330 fs/buffer.c:1562
 ext4_block_write_begin+0x164/0xb60 fs/ext4/inode.c:1042
 ext4_da_write_begin+0x4e8/0xa30 fs/ext4/inode.c:2997
 generic_perform_write+0x196/0x390 mm/filemap.c:3299
 ext4_buffered_write_iter+0x2cc/0x3b0 fs/ext4/file.c:270
 ext4_file_write_iter+0x76f/0x1010 include/linux/fs.h:804
 call_write_iter include/linux/fs.h:1907 [inline]
 new_sync_write fs/read_write.c:484 [inline]
 __vfs_write+0x2d8/0x340 fs/read_write.c:497
 vfs_write+0x19b/0x350 fs/read_write.c:559
 ksys_write+0xce/0x180 fs/read_write.c:612
 __do_sys_write fs/read_write.c:624 [inline]
 __se_sys_write fs/read_write.c:621 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:621
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10815 Comm: syz-executor.2 Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================