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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff88812a2a4650 of 8 bytes by task 28862 on cpu 0:
 __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:1721
 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
 sb_getblk include/linux/buffer_head.h:325 [inline]
 ext4_getblk+0xd5/0x2e0 fs/ext4/inode.c:839
 ext4_bread+0x3a/0x1f0 fs/ext4/inode.c:882
 ext4_append+0xda/0x1c0 fs/ext4/namei.c:67
 ext4_init_new_dir fs/ext4/namei.c:2765 [inline]
 ext4_mkdir+0x4b6/0xc90 fs/ext4/namei.c:2810
 vfs_mkdir+0x288/0x350 fs/namei.c:3649
 do_mkdirat+0x132/0x220 fs/namei.c:3672
 __do_sys_mkdir fs/namei.c:3688 [inline]
 __se_sys_mkdir fs/namei.c:3686 [inline]
 __x64_sys_mkdir+0x32/0x40 fs/namei.c:3686
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812a2a4650 of 8 bytes by task 23834 on cpu 1:
 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: 1 PID: 23834 Comm: kworker/1:12 Not tainted 5.9.0-rc2-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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