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BUG: KCSAN: data-race in __add_to_page_cache_locked / nr_blockdev_pages

write to 0xffff88812b803970 of 8 bytes by task 16032 on cpu 1:
 __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:1656
 find_or_create_page include/linux/pagemap.h:308 [inline]
 grow_dev_page fs/buffer.c:983 [inline]
 grow_buffers fs/buffer.c:1052 [inline]
 __getblk_slow fs/buffer.c:1079 [inline]
 __getblk_gfp+0x1f3/0x560 fs/buffer.c:1356
 __bread_gfp+0x34/0x1d0 fs/buffer.c:1390
 sb_bread include/linux/buffer_head.h:307 [inline]
 fat__get_entry+0x379/0x510 fs/fat/dir.c:100
 fat_get_entry fs/fat/dir.c:128 [inline]
 fat_get_short_entry+0xd4/0x1d0 fs/fat/dir.c:877
 fat_subdirs+0x6a/0x110 fs/fat/dir.c:943
 fat_read_root fs/fat/inode.c:1414 [inline]
 fat_fill_super+0x132f/0x1c90 fs/fat/inode.c:1858
 vfat_fill_super+0x37/0x50 fs/fat/namei_vfat.c:1050
 mount_bdev+0x264/0x2d0 fs/super.c:1417
 vfat_mount+0x38/0x50 fs/fat/namei_vfat.c:1057
 legacy_get_tree+0x78/0xf0 fs/fs_context.c:622
 vfs_get_tree+0x52/0x190 fs/super.c:1547
 do_new_mount fs/namespace.c:2816 [inline]
 do_mount+0xff0/0x1590 fs/namespace.c:3141
 __do_sys_mount fs/namespace.c:3350 [inline]
 __se_sys_mount fs/namespace.c:3327 [inline]
 __x64_sys_mount+0x12b/0x1a0 fs/namespace.c:3327
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812b803970 of 8 bytes by task 16031 on cpu 0:
 nr_blockdev_pages+0x6c/0xc0 fs/block_dev.c:953
 si_meminfo+0x3a/0x60 mm/page_alloc.c:5197
 do_sysinfo+0x128/0x350 kernel/sys.c:2557
 __do_sys_sysinfo+0x33/0x90 kernel/sys.c:2608
 __se_sys_sysinfo kernel/sys.c:2604 [inline]
 __x64_sys_sysinfo+0x27/0x40 kernel/sys.c:2604
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16031 Comm: syz-executor.4 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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