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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

read-write to 0xffff88810c298810 of 8 bytes by task 19725 on cpu 0:
 __add_to_page_cache_locked+0x39d/0x7b0 mm/filemap.c:888
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:939
 pagecache_get_page+0x60f/0x980 mm/filemap.c:1839
 grab_cache_page_write_begin+0x3f/0x70 mm/filemap.c:3475
 block_write_begin+0x33/0x1b0 fs/buffer.c:2116
 blkdev_write_begin+0x37/0x40 fs/block_dev.c:644
 generic_perform_write+0x196/0x3a0 mm/filemap.c:3525
 __generic_file_write_iter+0x15c/0x330 mm/filemap.c:3654
 blkdev_write_iter+0x1f4/0x2a0 fs/block_dev.c:1905
 call_write_iter include/linux/fs.h:1887 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0x630/0x6b0 fs/read_write.c:586
 ksys_write+0xce/0x180 fs/read_write.c:639
 __do_sys_write fs/read_write.c:651 [inline]
 __se_sys_write fs/read_write.c:648 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:648
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810c298810 of 8 bytes by task 16787 on cpu 1:
 nr_blockdev_pages+0x7c/0xd0 fs/block_dev.c:946
 si_meminfo+0x3a/0x60 mm/page_alloc.c:5330
 update_defense_level+0x34/0x550 net/netfilter/ipvs/ip_vs_ctl.c:101
 defense_work_handler+0x1b/0x80 net/netfilter/ipvs/ip_vs_ctl.c:235
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
 worker_thread+0x635/0xb90 kernel/workqueue.c:2418
 kthread+0x1ff/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: 16787 Comm: kworker/1:5 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_long defense_work_handler
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