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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff88812a736628 of 8 bytes by task 12782 on cpu 0:
 __add_to_page_cache_locked+0x28a/0x770 mm/filemap.c:868
 add_to_page_cache_lru+0xc7/0x260 mm/filemap.c:921
 mpage_readpages+0x23c/0x370 fs/mpage.c:399
 blkdev_readpages+0x32/0x50 fs/block_dev.c:620
 read_pages+0xa2/0x2d0 mm/readahead.c:126
 __do_page_cache_readahead+0x358/0x380 mm/readahead.c:212
 ra_submit mm/internal.h:62 [inline]
 do_sync_mmap_readahead mm/filemap.c:2400 [inline]
 filemap_fault+0xeeb/0x1120 mm/filemap.c:2486
 __do_fault+0xa8/0x1e0 mm/memory.c:3276
 do_shared_fault mm/memory.c:3728 [inline]
 do_fault mm/memory.c:3806 [inline]
 handle_pte_fault mm/memory.c:4033 [inline]
 __handle_mm_fault+0x1d2d/0x2cf0 mm/memory.c:4163
 handle_mm_fault+0x21c/0x540 mm/memory.c:4200
 do_user_addr_fault arch/x86/mm/fault.c:1442 [inline]
 do_page_fault+0x4a4/0xa52 arch/x86/mm/fault.c:1517
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203

read to 0xffff88812a736628 of 8 bytes by task 7801 on cpu 1:
 nr_blockdev_pages+0x6c/0xc0 fs/block_dev.c:952
 si_meminfo+0x3a/0x60 mm/page_alloc.c:5126
 update_defense_level+0x4a/0xa80 net/netfilter/ipvs/ip_vs_ctl.c:101
 defense_work_handler+0x3a/0xd0 net/netfilter/ipvs/ip_vs_ctl.c:224
 process_one_work+0x424/0x930 kernel/workqueue.c:2264
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2410
 kthread+0x1cb/0x1f0 kernel/kthread.c:255
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7801 Comm: kworker/1:3 Not tainted 5.6.0-rc1-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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