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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff88821aa0f6b0 of 8 bytes by task 11412 on cpu 1:
 __add_to_page_cache_locked+0x2cc/0x6e0 mm/filemap.c:867
 add_to_page_cache_lru+0xa0/0x1b0 mm/filemap.c:918
 pagecache_get_page+0x552/0x8b0 mm/filemap.c:1653
 find_or_create_page include/linux/pagemap.h:348 [inline]
 grow_dev_page+0x78/0x3e0 fs/buffer.c:975
 grow_buffers fs/buffer.c:1044 [inline]
 __getblk_slow fs/buffer.c:1071 [inline]
 __getblk_gfp+0x13b/0x1f0 fs/buffer.c:1355
 sb_getblk include/linux/buffer_head.h:325 [inline]
 __ext4_get_inode_loc+0x20c/0x9a0 fs/ext4/inode.c:4284
 ext4_get_inode_loc fs/ext4/inode.c:4402 [inline]
 ext4_reserve_inode_write+0x8b/0x150 fs/ext4/inode.c:5643
 __ext4_mark_inode_dirty+0x6e/0x630 fs/ext4/inode.c:5810
 ext4_ext_tree_init+0x7e/0x90 fs/ext4/extents.c:834
 __ext4_new_inode+0x2990/0x2fc0 fs/ext4/ialloc.c:1184
 ext4_symlink+0x354/0x7e0 fs/ext4/namei.c:3303
 vfs_symlink+0x218/0x2f0 fs/namei.c:3953
 do_symlinkat+0xee/0x280 fs/namei.c:3980
 __do_sys_symlink fs/namei.c:3999 [inline]
 __se_sys_symlink fs/namei.c:3997 [inline]
 __x64_sys_symlink+0x32/0x40 fs/namei.c:3997
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88821aa0f6b0 of 8 bytes by task 9686 on cpu 0:
 nr_blockdev_pages+0x6c/0xb0 fs/block_dev.c:933
 si_meminfo+0x3a/0x60 mm/page_alloc.c:5238
 update_defense_level+0x34/0x550 net/netfilter/ipvs/ip_vs_ctl.c:101
 defense_work_handler+0x1a/0x80 net/netfilter/ipvs/ip_vs_ctl.c:224
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9686 Comm: kworker/0:4 Not tainted 5.8.0-rc5-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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