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BUG: KCSAN: data-race in __filemap_add_folio / nr_blockdev_pages

read-write to 0xffff88810048bb78 of 8 bytes by task 27730 on cpu 1:
 __filemap_add_folio+0x671/0x880 mm/filemap.c:920
 filemap_add_folio+0x1d3/0x350 mm/filemap.c:967
 __filemap_get_folio_mpol+0x326/0x680 mm/filemap.c:2022
 __filemap_get_folio include/linux/pagemap.h:763 [inline]
 grow_dev_folio fs/buffer.c:954 [inline]
 grow_buffers fs/buffer.c:1020 [inline]
 __getblk_slow fs/buffer.c:1038 [inline]
 bdev_getblk+0x173/0x3f0 fs/buffer.c:1358
 __getblk include/linux/buffer_head.h:380 [inline]
 sb_getblk include/linux/buffer_head.h:386 [inline]
 ext4_read_block_bitmap_nowait+0x168/0x680 fs/ext4/balloc.c:488
 ext4_mb_prefetch+0x143/0x230 fs/ext4/mballoc.c:2878
 ext4_mb_might_prefetch fs/ext4/mballoc.c:2918 [inline]
 ext4_mb_scan_group+0x183/0xf20 fs/ext4/mballoc.c:2963
 ext4_mb_scan_groups_linear fs/ext4/mballoc.c:1176 [inline]
 ext4_mb_scan_groups fs/ext4/mballoc.c:1208 [inline]
 ext4_mb_regular_allocator+0x677/0x16a0 fs/ext4/mballoc.c:3062
 ext4_mb_new_blocks+0x7db/0x1e90 fs/ext4/mballoc.c:6310
 ext4_alloc_branch fs/ext4/indirect.c:340 [inline]
 ext4_ind_map_blocks+0xbfa/0x15a0 fs/ext4/indirect.c:635
 ext4_map_create_blocks+0x8a/0x3a0 fs/ext4/inode.c:633
 ext4_map_blocks+0x594/0x970 fs/ext4/inode.c:824
 _ext4_get_block+0x117/0x370 fs/ext4/inode.c:924
 ext4_get_block+0x39/0x50 fs/ext4/inode.c:941
 ext4_block_write_begin+0x650/0xcf0 fs/ext4/inode.c:1211
 ext4_convert_inline_data_to_extent+0x3e2/0x7d0 fs/ext4/ext4_jbd2.h:-1
 ext4_try_to_write_inline_data+0x54/0x90 fs/ext4/inline.c:789
 ext4_write_begin+0x1a6/0xe50 fs/ext4/inode.c:1315
 ext4_da_write_begin+0x1ef/0x680 fs/ext4/inode.c:3152
 generic_perform_write+0x183/0x490 mm/filemap.c:4325
 ext4_buffered_write_iter+0x304/0x4c0 fs/ext4/file.c:316
 ext4_file_write_iter+0x380/0xfa0 fs/ext4/file.c:-1
 do_iter_readv_writev+0x4fd/0x5a0 fs/read_write.c:-1
 vfs_writev+0x2e1/0x900 fs/read_write.c:1059
 do_pwritev fs/read_write.c:1155 [inline]
 __do_sys_pwritev2 fs/read_write.c:1213 [inline]
 __se_sys_pwritev2+0xfc/0x1c0 fs/read_write.c:1204
 __x64_sys_pwritev2+0x67/0x80 fs/read_write.c:1204
 x64_sys_call+0xe07/0x3020 arch/x86/include/generated/asm/syscalls_64.h:329
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810048bb78 of 8 bytes by task 3903 on cpu 0:
 nr_blockdev_pages+0x7e/0xd0 block/bdev.c:531
 si_meminfo+0x87/0xd0 mm/show_mem.c:80
 update_defense_level+0x47/0x5d0 net/netfilter/ipvs/ip_vs_ctl.c:102
 defense_work_handler+0x1f/0x80 net/netfilter/ipvs/ip_vs_ctl.c:235
 process_one_work kernel/workqueue.c:3302 [inline]
 process_scheduled_works+0x4f0/0x9c0 kernel/workqueue.c:3385
 worker_thread+0x58a/0x780 kernel/workqueue.c:3466
 kthread+0x22a/0x280 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 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: 0 UID: 0 PID: 3903 Comm: kworker/0:9 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: events_long defense_work_handler
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