syzbot

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BUG: KCSAN: data-race in __xa_set_mark / xas_find_marked

read-write to 0xffff8881071c4228 of 8 bytes by task 3295 on cpu 0:
 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+0xd2/0x1a0 lib/xarray.c:2079
 __folio_mark_dirty+0x3af/0x4d0 mm/page-writeback.c:2744
 mark_buffer_dirty+0x11e/0x210 fs/buffer.c:1212
 block_commit_write fs/buffer.c:2224 [inline]
 block_page_mkwrite+0x287/0x3d0 fs/buffer.c:2650
 ext4_page_mkwrite+0x76b/0xba0 fs/ext4/inode.c:6598
 do_page_mkwrite mm/memory.c:3378 [inline]
 wp_page_shared mm/memory.c:3779 [inline]
 do_wp_page+0xe5d/0x2400 mm/memory.c:3998
 handle_pte_fault mm/memory.c:6085 [inline]
 __handle_mm_fault mm/memory.c:6212 [inline]
 handle_mm_fault+0x77d/0x2be0 mm/memory.c:6381
 do_user_addr_fault+0x636/0x1090 arch/x86/mm/fault.c:1336
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x62/0xa0 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623

read to 0xffff8881071c4228 of 8 bytes by task 7700 on cpu 1:
 xas_find_chunk include/linux/xarray.h:1752 [inline]
 xas_find_marked+0x218/0x620 lib/xarray.c:1510
 find_get_entry+0x5d/0x380 mm/filemap.c:2038
 filemap_get_folios_tag+0x92/0x210 mm/filemap.c:2306
 mpage_prepare_extent_to_map+0x320/0xaa0 fs/ext4/inode.c:2577
 ext4_do_writepages+0x6ea/0x21c0 fs/ext4/inode.c:2816
 ext4_writepages+0x176/0x300 fs/ext4/inode.c:2953
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2636
 __writeback_single_inode+0x80/0x7c0 fs/fs-writeback.c:1680
 writeback_sb_inodes+0x480/0xa20 fs/fs-writeback.c:1976
 __writeback_inodes_wb+0x94/0x1a0 fs/fs-writeback.c:2047
 wb_writeback+0x266/0x5c0 fs/fs-writeback.c:2158
 wb_check_old_data_flush fs/fs-writeback.c:2262 [inline]
 wb_do_writeback fs/fs-writeback.c:2315 [inline]
 wb_workfn+0x601/0x910 fs/fs-writeback.c:2343
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3321
 worker_thread+0x582/0x770 kernel/workqueue.c:3402
 kthread+0x486/0x510 kernel/kthread.c:464
 ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x0060000000000000 -> 0x0060000010000200

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 7700 Comm: kworker/u8:33 Not tainted 6.16.0-rc3-syzkaller-00190-g67a993863163 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: writeback wb_workfn (flush-8:0)
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