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BUG: KCSAN: data-race in wbc_detach_inode / wbc_detach_inode

read to 0xffff88812b87ec1e of 2 bytes by task 18522 on cpu 0:
 wbc_detach_inode+0x77/0x520 fs/fs-writeback.c:638
 __filemap_fdatawrite_range+0x1d4/0x230 mm/filemap.c:422
 __filemap_fdatawrite mm/filemap.c:429 [inline]
 filemap_flush+0x2d/0x40 mm/filemap.c:456
 __sync_blockdev fs/block_dev.c:490 [inline]
 __sync_blockdev+0x81/0x90 fs/block_dev.c:485
 __sync_filesystem fs/sync.c:40 [inline]
 sync_filesystem+0x116/0x1a0 fs/sync.c:64
 generic_shutdown_super+0x6b/0x260 fs/super.c:448
 kill_block_super+0x60/0xb0 fs/super.c:1442
 deactivate_locked_super+0x64/0xb0 fs/super.c:335
 deactivate_super fs/super.c:366 [inline]
 deactivate_super+0xca/0xe0 fs/super.c:362
 cleanup_mnt+0x27f/0x330 fs/namespace.c:1102
 __cleanup_mnt+0x1f/0x30 fs/namespace.c:1109
 task_work_run+0xf6/0x130 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2b4/0x2c0 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x384/0x3a0 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812b87ec1e of 2 bytes by task 21 on cpu 1:
 wbc_detach_inode+0x27c/0x520 fs/fs-writeback.c:706
 writeback_sb_inodes+0x4c6/0xa50 fs/fs-writeback.c:1718
 __writeback_inodes_wb+0xe8/0x1b0 fs/fs-writeback.c:1785
 wb_writeback+0x557/0x6a0 fs/fs-writeback.c:1894
 wb_check_background_flush fs/fs-writeback.c:1962 [inline]
 wb_do_writeback fs/fs-writeback.c:2050 [inline]
 wb_workfn+0x696/0x970 fs/fs-writeback.c:2078
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2264
 worker_thread+0xa0/0x800 kernel/workqueue.c:2410
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 21 Comm: kworker/u4:1 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-7:3)
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