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BUG: KCSAN: data-race in delete_from_page_cache_batch / nr_blockdev_pages

read-write to 0xffff8881411e1c10 of 8 bytes by task 13663 on cpu 0:
 page_cache_delete_batch mm/filemap.c:340 [inline]
 delete_from_page_cache_batch+0x58b/0x810 mm/filemap.c:358
 truncate_inode_pages_range+0x482/0x10c0 mm/truncate.c:366
 truncate_inode_pages+0x20/0x30 mm/truncate.c:476
 kill_bdev fs/block_dev.c:87 [inline]
 __blkdev_put+0x23c/0x450 fs/block_dev.c:1563
 blkdev_put+0x212/0x290 fs/block_dev.c:1623
 blkdev_close+0x47/0x50 fs/block_dev.c:1631
 __fput+0x24b/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0x8e/0x110 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+0x16b/0x1a0 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881411e1c10 of 8 bytes by task 3968 on cpu 1:
 nr_blockdev_pages+0x7c/0xd0 fs/block_dev.c:932
 si_meminfo+0x3a/0x60 mm/page_alloc.c:5399
 update_balloon_stats drivers/virtio/virtio_balloon.c:330 [inline]
 stats_handle_request drivers/virtio/virtio_balloon.c:386 [inline]
 update_balloon_stats_func+0x41/0x2e0 drivers/virtio/virtio_balloon.c:472
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3968 Comm: kworker/1:0 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_freezable update_balloon_stats_func
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