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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff88812b86b310 of 8 bytes by task 17627 on cpu 1:
 __add_to_page_cache_locked+0x2cc/0x710 mm/filemap.c:868
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:919
 pagecache_get_page+0x570/0x970 mm/filemap.c:1819
 find_or_create_page include/linux/pagemap.h:348 [inline]
 grow_dev_page+0x78/0x410 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+0x1833/0x3020 fs/reiserfs/journal.c:2881
 reiserfs_fill_super+0x850/0x1bb0 fs/reiserfs/super.c:2032
 mount_bdev+0x1e8/0x290 fs/super.c:1417
 get_super_block+0x2d/0x40 fs/reiserfs/super.c:2606
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4d/0x1a0 fs/super.c:1547
 do_new_mount fs/namespace.c:2875 [inline]
 path_mount+0x118d/0x1c70 fs/namespace.c:3192
 do_mount fs/namespace.c:3205 [inline]
 __do_sys_mount fs/namespace.c:3413 [inline]
 __se_sys_mount+0x126/0x180 fs/namespace.c:3390
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3390
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812b86b310 of 8 bytes by task 6634 on cpu 0:
 nr_blockdev_pages+0x7c/0xd0 fs/block_dev.c:914
 si_meminfo+0x3a/0x60 mm/page_alloc.c:5263
 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+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/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: 6634 Comm: kworker/0:2 Not tainted 5.9.0-rc7-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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