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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff888125253a28 of 8 bytes by task 8818 on cpu 0:
 __add_to_page_cache_locked+0x28a/0x770 mm/filemap.c:868
 add_to_page_cache_lru+0xc7/0x260 mm/filemap.c:921
 pagecache_get_page+0x2b0/0x700 mm/filemap.c:1660
 find_or_create_page include/linux/pagemap.h:310 [inline]
 grow_dev_page fs/buffer.c:989 [inline]
 grow_buffers fs/buffer.c:1058 [inline]
 __getblk_slow fs/buffer.c:1085 [inline]
 __getblk_gfp+0x1f3/0x560 fs/buffer.c:1362
 __bread_gfp+0x34/0x1d0 fs/buffer.c:1396
 sb_bread include/linux/buffer_head.h:307 [inline]
 isofs_bread+0x7b/0x90 fs/isofs/inode.c:1180
 isofs_find_entry fs/isofs/namei.c:59 [inline]
 isofs_lookup+0x620/0x81e fs/isofs/namei.c:164
 lookup_open fs/namei.c:3288 [inline]
 do_last fs/namei.c:3401 [inline]
 path_openat+0x15ce/0x2f70 fs/namei.c:3607
 do_filp_open+0x11e/0x1b0 fs/namei.c:3637
 do_sys_openat2+0x4f5/0x620 fs/open.c:1149
 do_sys_open+0xa2/0x110 fs/open.c:1165
 __do_sys_openat fs/open.c:1179 [inline]
 __se_sys_openat fs/open.c:1174 [inline]
 __x64_sys_openat+0x5d/0x70 fs/open.c:1174
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888125253a28 of 8 bytes by task 988 on cpu 1:
 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: 1 PID: 988 Comm: kworker/1:0 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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