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BUG: KCSAN: data-race in xas_clear_mark / xas_find_marked

read-write to 0xffff888107f2c6c8 of 8 bytes by task 6982 on cpu 1:
 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_clear_bit include/asm-generic/bitops/instrumented-non-atomic.h:114 [inline]
 node_clear_mark lib/xarray.c:102 [inline]
 xas_clear_mark+0x91/0x180 lib/xarray.c:922
 __folio_start_writeback+0x270/0x370 mm/page-writeback.c:3032
 __block_write_full_folio+0x53a/0x8f0 fs/buffer.c:1825
 block_write_full_folio+0x2c1/0x2e0 fs/buffer.c:-1
 blkdev_writepages+0x88/0x100 block/fops.c:486
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2575
 filemap_writeback mm/filemap.c:388 [inline]
 filemap_fdatawrite_range mm/filemap.c:413 [inline]
 filemap_write_and_wait_range+0x166/0x370 mm/filemap.c:685
 filemap_write_and_wait include/linux/pagemap.h:65 [inline]
 sync_blockdev block/bdev.c:276 [inline]
 bdev_release+0xeb/0x3d0 block/bdev.c:1134
 blkdev_release+0x15/0x20 block/fops.c:705
 __fput+0x29b/0x630 fs/file_table.c:510
 ____fput+0x1c/0x30 fs/file_table.c:538
 task_work_run+0x130/0x1a0 kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x4ae/0x1530 kernel/exit.c:975
 do_group_exit+0xfe/0x140 kernel/exit.c:1117
 get_signal+0xe30/0xf20 kernel/signal.c:3037
 arch_do_signal_or_restart+0x96/0x450 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0x6a/0x6f0 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
 do_syscall_64+0x232/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888107f2c6c8 of 8 bytes by task 7041 on cpu 0:
 xas_find_chunk include/linux/xarray.h:1752 [inline]
 xas_find_marked+0x213/0x620 lib/xarray.c:1510
 find_get_entry mm/filemap.c:2070 [inline]
 filemap_get_folios_tag+0xfa/0x430 mm/filemap.c:2338
 writeback_get_folio mm/page-writeback.c:2432 [inline]
 writeback_iter+0x4bb/0x800 mm/page-writeback.c:2533
 blkdev_writepages+0xa7/0x100 block/fops.c:485
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2575
 filemap_writeback mm/filemap.c:388 [inline]
 filemap_fdatawrite_range mm/filemap.c:413 [inline]
 filemap_fdatawrite+0x100/0x140 mm/filemap.c:419
 sync_bdevs+0x1a2/0x260 block/bdev.c:1308
 ksys_sync fs/sync.c:105 [inline]
 __ia32_sys_sync+0x81/0xb0 fs/sync.c:111
 x64_sys_call+0x2f3a/0x3020 arch/x86/include/generated/asm/syscalls_64.h:163
 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

value changed: 0xfffc000000000000 -> 0xffe0000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 7041 Comm: syz.3.866 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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