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BUG: KCSAN: data-race in __xa_clear_mark / xas_find_marked

write to 0xffff8881067a9fb0 of 8 bytes by interrupt on cpu 1:
 instrument_write include/linux/instrumented.h:42 [inline]
 __instrument_read_write_bitop include/asm-generic/bitops/instrumented-non-atomic.h:79 [inline]
 __test_and_clear_bit include/asm-generic/bitops/instrumented-non-atomic.h:109 [inline]
 node_clear_mark lib/xarray.c:100 [inline]
 xas_clear_mark lib/xarray.c:911 [inline]
 __xa_clear_mark+0x1d9/0x2c0 lib/xarray.c:1917
 test_clear_page_writeback+0x23e/0x560 mm/page-writeback.c:2736
 end_page_writeback+0xd7/0x1b0 mm/filemap.c:1548
 page_endio+0x1cc/0x280 mm/filemap.c:1580
 mpage_end_io+0x186/0x1d0 fs/mpage.c:54
 bio_endio+0x21d/0x300 block/bio.c:1414
 req_bio_endio block/blk-core.c:265 [inline]
 blk_update_request+0x435/0xa30 block/blk-core.c:1454
 blk_mq_end_request+0x22/0x50 block/blk-mq.c:565
 lo_complete_rq+0xca/0x170 drivers/block/loop.c:498
 blk_complete_reqs block/blk-mq.c:577 [inline]
 blk_done_softirq+0x69/0x90 block/blk-mq.c:582
 __do_softirq+0x12c/0x275 kernel/softirq.c:559
 run_ksoftirqd+0x13/0x20 kernel/softirq.c:921
 smpboot_thread_fn+0x2a1/0x3f0 kernel/smpboot.c:165
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881067a9fb0 of 8 bytes by task 7801 on cpu 0:
 xas_find_chunk include/linux/xarray.h:1662 [inline]
 xas_find_marked+0x195/0x5f0 lib/xarray.c:1349
 find_get_entry mm/filemap.c:1925 [inline]
 find_get_pages_range_tag+0xf2/0x390 mm/filemap.c:2216
 pagevec_lookup_range_tag+0x37/0x50 mm/swap.c:1123
 __filemap_fdatawait_range+0xab/0x1b0 mm/filemap.c:510
 filemap_fdatawait_keep_errors+0x24/0x80 mm/filemap.c:613
 wait_sb_inodes fs/fs-writeback.c:2458 [inline]
 sync_inodes_sb+0x3f6/0x4d0 fs/fs-writeback.c:2580
 sync_inodes_one_sb+0x39/0x50 fs/sync.c:74
 iterate_supers+0x137/0x1f0 fs/super.c:695
 ksys_sync+0x59/0xe0 fs/sync.c:114
 __do_sys_sync+0xa/0x10 fs/sync.c:125
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7801 Comm: syz-executor.5 Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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