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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff888128c4e368 of 8 bytes by task 19627 on cpu 1:
 __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]
 ondemand_readahead+0x369/0x730 mm/readahead.c:492
 page_cache_async_readahead+0x237/0x260 mm/readahead.c:574
 do_async_mmap_readahead mm/filemap.c:2425 [inline]
 filemap_fault+0x866/0x1120 mm/filemap.c:2480
 __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
 faultin_page mm/gup.c:659 [inline]
 __get_user_pages+0x485/0x1140 mm/gup.c:870
 __get_user_pages_locked mm/gup.c:1057 [inline]
 get_user_pages_unlocked+0x24a/0x420 mm/gup.c:1765
 __gup_longterm_unlocked mm/gup.c:2423 [inline]
 internal_get_user_pages_fast mm/gup.c:2464 [inline]
 get_user_pages_fast+0x32d/0x350 mm/gup.c:2505
 iov_iter_get_pages+0x1d3/0x8cc lib/iov_iter.c:1323
 __bio_iov_iter_get_pages block/bio.c:939 [inline]
 bio_iov_iter_get_pages+0x106/0x5a0 block/bio.c:995
 __blkdev_direct_IO fs/block_dev.c:386 [inline]
 blkdev_direct_IO+0x5e3/0xab0 fs/block_dev.c:476
 generic_file_read_iter+0x1aa/0x1490 mm/filemap.c:2281
 blkdev_read_iter+0xae/0xe0 fs/block_dev.c:2039
 call_read_iter include/linux/fs.h:1895 [inline]
 do_iter_readv_writev+0x570/0x5d0 fs/read_write.c:691
 do_iter_read+0x1e4/0x3a0 fs/read_write.c:933
 vfs_readv+0x9c/0xf0 fs/read_write.c:1053
 do_preadv+0x129/0x1c0 fs/read_write.c:1145
 __do_sys_preadv fs/read_write.c:1195 [inline]
 __se_sys_preadv fs/read_write.c:1190 [inline]
 __x64_sys_preadv+0x5e/0x80 fs/read_write.c:1190
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888128c4e368 of 8 bytes by task 3645 on cpu 0:
 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: 0 PID: 3645 Comm: kworker/0:3 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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