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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff888120673ef0 of 8 bytes by task 21448 on cpu 0:
 __add_to_page_cache_locked+0x2cc/0x6e0 mm/filemap.c:867
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:918
 page_cache_readahead_unbounded+0x234/0x440 mm/readahead.c:228
 ondemand_readahead+0x4e4/0x6e0 mm/readahead.c:273
 page_cache_async_readahead+0x1c6/0x1e0 mm/readahead.c:631
 do_async_mmap_readahead mm/filemap.c:2430 [inline]
 filemap_fault+0x2f1/0x11e0 mm/filemap.c:2485
 __do_fault mm/memory.c:3464 [inline]
 do_read_fault+0x41f/0x730 mm/memory.c:3857
 do_fault mm/memory.c:3985 [inline]
 handle_pte_fault mm/memory.c:4225 [inline]
 __handle_mm_fault mm/memory.c:4357 [inline]
 handle_mm_fault+0x135d/0x1930 mm/memory.c:4394
 faultin_page mm/gup.c:887 [inline]
 __get_user_pages+0xac6/0x1150 mm/gup.c:1113
 populate_vma_page_range mm/gup.c:1452 [inline]
 __mm_populate+0x256/0x340 mm/gup.c:1500
 mm_populate include/linux/mm.h:2605 [inline]
 vm_mmap_pgoff+0x13b/0x170 mm/util.c:511
 ksys_mmap_pgoff+0x342/0x3a0 mm/mmap.c:1595
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888120673ef0 of 8 bytes by task 12424 on cpu 1:
 nr_blockdev_pages+0x6c/0xb0 fs/block_dev.c:933
 si_meminfo+0x3a/0x60 mm/page_alloc.c:5238
 update_defense_level+0x34/0x550 net/netfilter/ipvs/ip_vs_ctl.c:101
 defense_work_handler+0x1a/0x80 net/netfilter/ipvs/ip_vs_ctl.c:224
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12424 Comm: kworker/1:6 Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events defense_work_handler
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