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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff888140478e10 of 8 bytes by task 18704 on cpu 1:
 __add_to_page_cache_locked+0x3ad/0x6e0 mm/filemap.c:890
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:943
 page_cache_ra_unbounded+0x272/0x4c0 mm/readahead.c:222
 do_page_cache_ra mm/readahead.c:267 [inline]
 force_page_cache_ra+0x226/0x260 mm/readahead.c:298
 page_cache_sync_ra+0x178/0x1a0 mm/readahead.c:572
 page_cache_sync_readahead include/linux/pagemap.h:839 [inline]
 generic_file_buffered_read_get_pages+0x234/0xaf0 mm/filemap.c:2365
 generic_file_buffered_read+0x26e/0x9c0 mm/filemap.c:2485
 generic_file_read_iter+0x82/0x3e0 mm/filemap.c:2637
 blkdev_read_iter+0xb3/0xc0 fs/block_dev.c:1714
 call_read_iter include/linux/fs.h:1895 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x565/0x5d0 fs/read_write.c:496
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888140478e10 of 8 bytes by task 12260 on cpu 0:
 nr_blockdev_pages+0x7c/0xd0 fs/block_dev.c:942
 si_meminfo+0x3a/0x60 mm/page_alloc.c:5404
 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:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12260 Comm: kworker/0:5 Not tainted 5.11.0-rc6-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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