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BUG: KCSAN: data-race in __xa_clear_mark / xas_find_marked

read-write to 0xffff88811b0e1900 of 8 bytes by interrupt 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 lib/xarray.c:922 [inline]
 __xa_clear_mark+0xf5/0x1e0 lib/xarray.c:2100
 __folio_end_writeback+0xf4/0x360 mm/page-writeback.c:2948
 folio_end_writeback_no_dropbehind+0x6d/0x1d0 mm/filemap.c:1666
 folio_end_writeback+0x1c/0x70 mm/filemap.c:1692
 ext4_finish_bio+0x459/0x8b0 fs/ext4/page-io.c:145
 ext4_end_bio+0x27b/0x380 fs/ext4/page-io.c:393
 bio_endio+0x38a/0x420 block/bio.c:1792
 blk_update_request+0x338/0x740 block/blk-mq.c:1016
 scsi_end_request+0x53/0x4c0 drivers/scsi/scsi_lib.c:647
 scsi_io_completion+0x7f/0x1d0 drivers/scsi/scsi_lib.c:1088
 scsi_finish_command+0x1c7/0x1e0 drivers/scsi/scsi.c:198
 scsi_complete+0x155/0x4f0 drivers/scsi/scsi_lib.c:1568
 blk_complete_reqs block/blk-mq.c:1253 [inline]
 blk_done_softirq+0x77/0xb0 block/blk-mq.c:1258
 handle_softirqs+0xb9/0x2a0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x39/0xc0 kernel/softirq.c:723
 common_interrupt+0x83/0x90 arch/x86/kernel/irq.c:326
 asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
 __preempt_count_dec_and_test arch/x86/include/asm/preempt.h:95 [inline]
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:179 [inline]
 _raw_spin_unlock_irqrestore+0x1a/0x30 kernel/locking/spinlock.c:194
 spin_unlock_irqrestore include/linux/spinlock.h:407 [inline]
 barn_replace_empty_sheaf+0xa8/0xf0 mm/slub.c:3202
 __pcs_replace_empty_main+0x7e/0x350 mm/slub.c:4593
 alloc_from_pcs mm/slub.c:4720 [inline]
 slab_alloc_node mm/slub.c:4854 [inline]
 __do_kmalloc_node mm/slub.c:5262 [inline]
 __kmalloc_node_track_caller_noprof+0x388/0x560 mm/slub.c:5371
 kmemdup_noprof+0x2b/0x70 mm/util.c:138
 kmemdup_noprof include/linux/fortify-string.h:763 [inline]
 __ip_vs_lblc_init+0x4d/0x180 net/netfilter/ipvs/ip_vs_lblc.c:558
 ops_init+0x22a/0x2e0 net/core/net_namespace.c:137
 setup_net+0x9f/0x230 net/core/net_namespace.c:446
 copy_net_ns+0x310/0x450 net/core/net_namespace.c:581
 create_new_namespaces+0x20e/0x440 kernel/nsproxy.c:130
 unshare_nsproxy_namespaces+0xe6/0x120 kernel/nsproxy.c:226
 ksys_unshare+0x3f2/0x6f0 kernel/fork.c:3174
 __do_sys_unshare kernel/fork.c:3245 [inline]
 __se_sys_unshare kernel/fork.c:3243 [inline]
 __x64_sys_unshare+0x1f/0x30 kernel/fork.c:3243
 x64_sys_call+0x1cef/0x3020 arch/x86/include/generated/asm/syscalls_64.h:273
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811b0e1900 of 8 bytes by task 4930 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:2069 [inline]
 filemap_get_folios_tag+0xfa/0x510 mm/filemap.c:2337
 __filemap_fdatawait_range mm/filemap.c:523 [inline]
 filemap_fdatawait_keep_errors+0x6c/0x190 mm/filemap.c:626
 wait_sb_inodes fs/fs-writeback.c:2805 [inline]
 sync_inodes_sb+0x40e/0x4c0 fs/fs-writeback.c:2927
 sync_inodes_one_sb+0x3d/0x50 fs/sync.c:77
 __iterate_supers+0x110/0x220 fs/super.c:927
 iterate_supers+0x1f/0x30 fs/super.c:942
 ksys_sync fs/sync.c:102 [inline]
 __ia32_sys_sync+0x5c/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/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000001 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 4930 Comm: syz.3.396 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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