syzbot

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BUG: KCSAN: data-race in __xa_set_mark / xas_find_marked

read-write to 0xffff88810651cb48 of 8 bytes by task 3288 on cpu 1:
 instrument_read_write include/linux/instrumented.h:55 [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+0xea/0x1c0 lib/xarray.c:2076
 __folio_mark_dirty+0x3b8/0x4e0 mm/page-writeback.c:2767
 mark_buffer_dirty+0x134/0x230 fs/buffer.c:1196
 block_commit_write fs/buffer.c:2189 [inline]
 block_page_mkwrite+0x295/0x3f0 fs/buffer.c:2615
 ext4_page_mkwrite+0x756/0xb90 fs/ext4/inode.c:6213
 do_page_mkwrite mm/memory.c:3287 [inline]
 wp_page_shared mm/memory.c:3688 [inline]
 do_wp_page+0xe86/0x24e0 mm/memory.c:3907
 handle_pte_fault mm/memory.c:6013 [inline]
 __handle_mm_fault mm/memory.c:6140 [inline]
 handle_mm_fault+0xc6c/0x2e80 mm/memory.c:6309
 do_user_addr_fault arch/x86/mm/fault.c:1337 [inline]
 handle_page_fault arch/x86/mm/fault.c:1480 [inline]
 exc_page_fault+0x3b9/0x6a0 arch/x86/mm/fault.c:1538
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623

read to 0xffff88810651cb48 of 8 bytes by task 3733 on cpu 0:
 xas_find_chunk include/linux/xarray.h:1746 [inline]
 xas_find_marked+0x21d/0x660 lib/xarray.c:1510
 find_get_entry+0x54/0x390 mm/filemap.c:2027
 filemap_get_folios_tag+0x13e/0x220 mm/filemap.c:2294
 mpage_prepare_extent_to_map+0x332/0xb80 fs/ext4/inode.c:2452
 ext4_do_writepages+0x705/0x21d0 fs/ext4/inode.c:2691
 ext4_writepages+0x183/0x320 fs/ext4/inode.c:2828
 do_writepages+0x1d8/0x480 mm/page-writeback.c:2656
 __writeback_single_inode+0x89/0x850 fs/fs-writeback.c:1680
 writeback_sb_inodes+0x458/0xa10 fs/fs-writeback.c:1976
 __writeback_inodes_wb+0x9a/0x1a0 fs/fs-writeback.c:2047
 wb_writeback+0x276/0x650 fs/fs-writeback.c:2158
 wb_check_start_all fs/fs-writeback.c:2284 [inline]
 wb_do_writeback fs/fs-writeback.c:2310 [inline]
 wb_workfn+0x510/0x960 fs/fs-writeback.c:2343
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4de/0xa20 kernel/workqueue.c:3319
 worker_thread+0x52c/0x710 kernel/workqueue.c:3400
 kthread+0x4b7/0x540 kernel/kthread.c:464
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x8000080054038000 -> 0x8002180054138000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3733 Comm: kworker/u8:16 Not tainted 6.14.0-syzkaller-12456-gacc4d5ff0b61 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: writeback wb_workfn (flush-8:0)
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