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BUG: KCSAN: data-race in __xa_set_mark / xas_find_marked

read-write to 0xffff888107b8a470 of 8 bytes by task 8976 on cpu 0:
 instrument_read_write include/linux/instrumented.h:56 [inline]
 __instrument_read_write_bitop include/asm-generic/bitops/instrumented-non-atomic.h:84 [inline]
 ___test_and_set_bit include/asm-generic/bitops/instrumented-non-atomic.h:99 [inline]
 node_set_mark lib/xarray.c:95 [inline]
 xas_set_mark lib/xarray.c:893 [inline]
 __xa_set_mark+0xd2/0x1a0 lib/xarray.c:2082
 __folio_mark_dirty+0x383/0x4a0 mm/page-writeback.c:2668
 mark_buffer_dirty+0x120/0x220 fs/buffer.c:1203
 block_commit_write fs/buffer.c:2215 [inline]
 block_page_mkwrite+0x287/0x3c0 fs/buffer.c:2640
 ext4_page_mkwrite+0x859/0xb90 fs/ext4/inode.c:6637
 do_page_mkwrite mm/memory.c:3589 [inline]
 do_shared_fault mm/memory.c:5874 [inline]
 do_fault mm/memory.c:5936 [inline]
 do_pte_missing mm/memory.c:4477 [inline]
 handle_pte_fault mm/memory.c:6316 [inline]
 __handle_mm_fault mm/memory.c:6454 [inline]
 handle_mm_fault+0x18f2/0x3020 mm/memory.c:6623
 do_user_addr_fault+0x62f/0x1050 arch/x86/mm/fault.c:1334
 handle_page_fault arch/x86/mm/fault.c:1474 [inline]
 exc_page_fault+0x62/0xa0 arch/x86/mm/fault.c:1527
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

read to 0xffff888107b8a470 of 8 bytes by task 3544 on cpu 1:
 xas_find_chunk include/linux/xarray.h:1752 [inline]
 xas_find_marked+0x213/0x620 lib/xarray.c:1510
 find_get_entry mm/filemap.c:2064 [inline]
 filemap_get_folios_tag+0xfa/0x510 mm/filemap.c:2332
 mpage_prepare_extent_to_map+0x328/0xc50 fs/ext4/inode.c:2632
 ext4_do_writepages+0x70f/0x2840 fs/ext4/inode.c:2871
 ext4_writepages+0x18f/0x320 fs/ext4/inode.c:3019
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2554
 __writeback_single_inode+0x80/0x860 fs/fs-writeback.c:1750
 writeback_sb_inodes+0x4fe/0xaf0 fs/fs-writeback.c:2042
 __writeback_inodes_wb+0x94/0x1a0 fs/fs-writeback.c:2118
 wb_writeback+0x272/0x5d0 fs/fs-writeback.c:2229
 wb_check_start_all fs/fs-writeback.c:2355 [inline]
 wb_do_writeback fs/fs-writeback.c:2381 [inline]
 wb_workfn+0x4fd/0x970 fs/fs-writeback.c:2414
 process_one_work kernel/workqueue.c:3275 [inline]
 process_scheduled_works+0x4de/0x9e0 kernel/workqueue.c:3358
 worker_thread+0x581/0x770 kernel/workqueue.c:3439
 kthread+0x22a/0x280 kernel/kthread.c:467
 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: 0x00000000003ff000 -> 0x0000000001fff000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3544 Comm: kworker/u8:8 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: writeback wb_workfn (flush-8:0)
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