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BUG: KCSAN: data-race in __filemap_add_folio / nr_blockdev_pages

read-write to 0xffff88810048dd08 of 8 bytes by task 27181 on cpu 0:
 __filemap_add_folio+0x671/0x8b0 mm/filemap.c:919
 filemap_add_folio+0x1d3/0x350 mm/filemap.c:966
 __filemap_get_folio_mpol+0x326/0x680 mm/filemap.c:2021
 __filemap_get_folio include/linux/pagemap.h:763 [inline]
 grow_dev_folio fs/buffer.c:1047 [inline]
 grow_buffers fs/buffer.c:1113 [inline]
 __getblk_slow fs/buffer.c:1131 [inline]
 bdev_getblk+0x173/0x3f0 fs/buffer.c:1458
 getblk_unmovable include/linux/buffer_head.h:369 [inline]
 ext4_getblk+0x1ca/0x530 fs/ext4/inode.c:1002
 ext4_bread+0x28/0x110 fs/ext4/inode.c:1050
 ext4_quota_read+0xe8/0x260 fs/ext4/super.c:7344
 v2_read_header fs/quota/quota_v2.c:62 [inline]
 v2_check_quota_file+0x72/0x160 fs/quota/quota_v2.c:81
 dquot_load_quota_sb+0x3ae/0x5e0 fs/quota/dquot.c:2455
 dquot_load_quota_inode+0x215/0x2f0 fs/quota/dquot.c:2499
 ext4_quota_enable fs/ext4/super.c:7227 [inline]
 ext4_enable_quotas+0x2d2/0x400 fs/ext4/super.c:7253
 __ext4_fill_super fs/ext4/super.c:5680 [inline]
 ext4_fill_super+0x3373/0x37c0 fs/ext4/super.c:5816
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1694
 get_tree_bdev+0x1f/0x30 fs/super.c:1717
 ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5848
 vfs_get_tree+0x57/0x1d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3763 [inline]
 do_new_mount+0x288/0x8d0 fs/namespace.c:3839
 path_mount+0x4d0/0xbc0 fs/namespace.c:4159
 do_mount fs/namespace.c:4172 [inline]
 __do_sys_mount fs/namespace.c:4361 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4338
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4338
 x64_sys_call+0x2d61/0x3020 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810048dd08 of 8 bytes by task 26645 on cpu 1:
 nr_blockdev_pages+0x7e/0xd0 block/bdev.c:539
 si_meminfo+0x87/0xd0 mm/show_mem.c:80
 update_defense_level+0x47/0x5d0 net/netfilter/ipvs/ip_vs_ctl.c:101
 defense_work_handler+0x1f/0x80 net/netfilter/ipvs/ip_vs_ctl.c:234
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0x513/0xa10 kernel/workqueue.c:3359
 worker_thread+0x58a/0x780 kernel/workqueue.c:3440
 kthread+0x22a/0x280 kernel/kthread.c:436
 ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x000000000000000b -> 0x000000000000000c

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 26645 Comm: kworker/1:2 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: events_long defense_work_handler
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