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BUG: KCSAN: data-race in xas_clear_mark / xas_find_marked

read-write to 0xffff88811b45b6c0 of 8 bytes by task 5831 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_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:3028
 mpage_write_folio fs/mpage.c:620 [inline]
 __mpage_writepages+0xdbd/0x1390 fs/mpage.c:686
 mpage_writepages include/linux/mpage.h:27 [inline]
 fat_writepages+0x26/0x30 fs/fat/inode.c:200
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2571
 filemap_writeback mm/filemap.c:388 [inline]
 filemap_fdatawrite_range mm/filemap.c:413 [inline]
 file_write_and_wait_range+0x178/0x2f0 mm/filemap.c:787
 mmb_fsync_noflush+0x48/0x140 fs/buffer.c:645
 fat_file_fsync+0x98/0x110 fs/fat/file.c:192
 vfs_fsync_range fs/sync.c:186 [inline]
 vfs_fsync fs/sync.c:200 [inline]
 do_fsync fs/sync.c:211 [inline]
 __do_sys_fdatasync fs/sync.c:221 [inline]
 __se_sys_fdatasync fs/sync.c:219 [inline]
 __x64_sys_fdatasync+0x83/0xe0 fs/sync.c:219
 x64_sys_call+0x2d1f/0x3020 arch/x86/include/generated/asm/syscalls_64.h:76
 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 0xffff88811b45b6c0 of 8 bytes by task 30 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:2070 [inline]
 filemap_get_folios_tag+0xfa/0x430 mm/filemap.c:2338
 writeback_get_folio mm/page-writeback.c:2428 [inline]
 writeback_iter+0x4bb/0x800 mm/page-writeback.c:2529
 __mpage_writepages+0x8a/0x1390 fs/mpage.c:675
 mpage_writepages include/linux/mpage.h:27 [inline]
 fat_writepages+0x26/0x30 fs/fat/inode.c:200
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2571
 __writeback_single_inode+0x7f/0x650 fs/fs-writeback.c:1764
 writeback_sb_inodes+0x4dd/0xaa0 fs/fs-writeback.c:2056
 wb_writeback+0x24e/0x560 fs/fs-writeback.c:2241
 wb_do_writeback fs/fs-writeback.c:2388 [inline]
 wb_workfn+0x194/0x930 fs/fs-writeback.c:2428
 process_one_work kernel/workqueue.c:3314 [inline]
 process_scheduled_works+0x4f0/0x9c0 kernel/workqueue.c:3397
 worker_thread+0x58a/0x780 kernel/workqueue.c:3478
 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: 0x000000001fffffe0 -> 0x000000001fffff80

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 30 Comm: kworker/u8:1 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: writeback wb_workfn (flush-7:0)
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