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BUG: KCSAN: data-race in iput / writeback_single_inode

write to 0xffff888105e8b6c8 of 8 bytes by task 1764 on cpu 1:
 writeback_single_inode+0x143/0x590 fs/fs-writeback.c:1577
 write_inode_now+0x129/0x150 fs/fs-writeback.c:2607
 bdev_write_inode fs/block_dev.c:65 [inline]
 __blkdev_put+0x2cb/0x490 fs/block_dev.c:1586
 blkdev_put+0x23e/0x2c0 fs/block_dev.c:1645
 kill_block_super+0x7b/0x90 fs/super.c:1397
 deactivate_locked_super+0x65/0xd0 fs/super.c:335
 deactivate_super+0x85/0x90 fs/super.c:366
 cleanup_mnt+0x277/0x2e0 fs/namespace.c:1136
 __cleanup_mnt+0x15/0x20 fs/namespace.c:1143
 task_work_run+0xae/0x130 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x151/0x170 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x40/0x50 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888105e8b6c8 of 8 bytes by task 1030 on cpu 0:
 iput+0x2e/0x590 fs/inode.c:1670
 bdput fs/block_dev.c:963 [inline]
 blkdev_put_no_open fs/block_dev.c:1402 [inline]
 blkdev_put+0x292/0x2c0 fs/block_dev.c:1646
 blkdev_close+0x47/0x50 fs/block_dev.c:1653
 __fput+0x25b/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0xae/0x130 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x151/0x170 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x40/0x50 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1030 Comm: systemd-udevd Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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