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BUG: KCSAN: data-race in __xa_clear_mark / xas_find_marked

write to 0xffff8881076b929c of 4 bytes by interrupt on cpu 0:
 xa_mark_clear lib/xarray.c:77 [inline]
 xas_clear_mark lib/xarray.c:932 [inline]
 __xa_clear_mark+0x1c6/0x1e0 lib/xarray.c:2100
 __folio_end_writeback+0xf4/0x360 mm/page-writeback.c:2971
 folio_end_writeback_no_dropbehind+0x6d/0x1d0 mm/filemap.c:1672
 folio_end_writeback+0x1c/0x70 mm/filemap.c:1698
 ext4_finish_bio+0x454/0x770 fs/ext4/page-io.c:144
 ext4_end_bio+0x281/0x3a0 fs/ext4/page-io.c:392
 bio_endio+0x35b/0x3f0 block/bio.c:1819
 blk_update_request+0x338/0x710 block/blk-mq.c:1016
 blk_mq_end_request+0x26/0x50 block/blk-mq.c:1147
 lo_complete_rq+0x98/0x130 drivers/block/loop.c:314
 blk_complete_reqs block/blk-mq.c:1222 [inline]
 blk_done_softirq+0x77/0xb0 block/blk-mq.c:1227
 handle_softirqs+0xb9/0x280 kernel/softirq.c:622
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:1076
 smpboot_thread_fn+0x32a/0x510 kernel/smpboot.c:160
 kthread+0x221/0x270 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

read to 0xffff8881076b929c of 4 bytes by task 4437 on cpu 1:
 xa_marked include/linux/xarray.h:424 [inline]
 xas_find_marked+0x602/0x650 lib/xarray.c:1483
 find_get_entry mm/filemap.c:2087 [inline]
 filemap_get_folios_tag+0xf7/0x400 mm/filemap.c:2354
 __filemap_fdatawait_range mm/filemap.c:523 [inline]
 file_write_and_wait_range+0x20c/0x2f0 mm/filemap.c:789
 ext4_sync_file+0x114/0x5c0 fs/ext4/fsync.c:145
 vfs_fsync_range+0xc5/0xe0 fs/sync.c:186
 generic_write_sync include/linux/fs.h:2672 [inline]
 ext4_buffered_write_iter+0x426/0x480 fs/ext4/file.c:324
 ext4_file_write_iter+0x38e/0xef0 fs/ext4/file.c:-1
 iter_file_splice_write+0x6a0/0xa60 fs/splice.c:736
 do_splice_from fs/splice.c:936 [inline]
 direct_splice_actor+0x156/0x280 fs/splice.c:1159
 splice_direct_to_actor+0x2f9/0x680 fs/splice.c:1103
 do_splice_direct_actor fs/splice.c:1202 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1228
 do_sendfile+0x37d/0x640 fs/read_write.c:1371
 __do_sys_sendfile64 fs/read_write.c:1432 [inline]
 __se_sys_sendfile64 fs/read_write.c:1418 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1418
 x64_sys_call+0x2e27/0x3050 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0e000021 -> 0x04000021

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 4437 Comm: syz.1.235 Tainted: G S                  syzkaller #0 PREEMPT(lazy) 
Tainted: [S]=CPU_OUT_OF_SPEC
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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