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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff888101e37bd0 of 8 bytes by task 3024 on cpu 1:
 __add_to_page_cache_locked+0x3ad/0x6e0 mm/filemap.c:887
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:940
 pagecache_get_page+0x6a0/0xa30 mm/filemap.c:1808
 find_or_create_page include/linux/pagemap.h:405 [inline]
 grow_dev_page+0x78/0x400 fs/buffer.c:974
 grow_buffers fs/buffer.c:1043 [inline]
 __getblk_slow fs/buffer.c:1070 [inline]
 __getblk_gfp+0x13b/0x1f0 fs/buffer.c:1354
 __getblk include/linux/buffer_head.h:380 [inline]
 reiserfs_breada fs/reiserfs/journal.c:2337 [inline]
 journal_read fs/reiserfs/journal.c:2447 [inline]
 journal_init+0x1890/0x3130 fs/reiserfs/journal.c:2881
 reiserfs_fill_super+0x850/0x1bc0 fs/reiserfs/super.c:2032
 mount_bdev+0x1e8/0x290 fs/super.c:1367
 get_super_block+0x2d/0x40 fs/reiserfs/super.c:2606
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4a/0x1a0 fs/super.c:1497
 do_new_mount fs/namespace.c:2903 [inline]
 path_mount+0x11b9/0x1c00 fs/namespace.c:3233
 do_mount fs/namespace.c:3246 [inline]
 __do_sys_mount fs/namespace.c:3454 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3431
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3431
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888101e37bd0 of 8 bytes by task 9841 on cpu 0:
 nr_blockdev_pages+0x7c/0xd0 fs/block_dev.c:951
 si_meminfo+0x3a/0x60 mm/page_alloc.c:5412
 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:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9841 Comm: kworker/0:9 Tainted: G        W         5.12.0-rc4-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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