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BUG: KCSAN: data-race in xas_clear_mark / xas_find_marked

write to 0xffff888125839b30 of 8 bytes by interrupt on cpu 1:
 __test_and_clear_bit include/asm-generic/bitops-instrumented.h:213 [inline]
 node_clear_mark lib/xarray.c:99 [inline]
 xas_clear_mark+0x11a/0x1d0 lib/xarray.c:907
 __xa_clear_mark+0xd3/0x100 lib/xarray.c:1713
 test_clear_page_writeback+0x449/0x790 mm/page-writeback.c:2731
 end_page_writeback+0x9e/0x190 mm/filemap.c:1338
 ext4_finish_bio+0x40d/0x520 fs/ext4/page-io.c:110
 ext4_end_bio+0xd2/0x310 fs/ext4/page-io.c:334
 bio_endio+0x3a8/0x4f0 block/bio.c:1818
 req_bio_endio block/blk-core.c:242 [inline]
 blk_update_request+0x427/0x7b0 block/blk-core.c:1462
 scsi_end_request+0x6b/0x3e0 drivers/scsi/scsi_lib.c:579
 scsi_io_completion+0x11d/0xc80 drivers/scsi/scsi_lib.c:963
 scsi_finish_command+0x280/0x380 drivers/scsi/scsi.c:228
 scsi_softirq_done+0x259/0x280 drivers/scsi/scsi_lib.c:1477
 blk_done_softirq+0x1eb/0x250 block/blk-softirq.c:37
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413

read to 0xffff888125839b30 of 8 bytes by task 7840 on cpu 0:
 xas_find_chunk include/linux/xarray.h:1590 [inline]
 xas_find_marked+0x17a/0x7b0 lib/xarray.c:1187
 find_get_pages_range_tag+0x111/0x670 mm/filemap.c:1924
 pagevec_lookup_range_tag+0x45/0x70 mm/swap.c:1054
 __filemap_fdatawait_range+0xdc/0x1d0 mm/filemap.c:517
 filemap_fdatawait_range mm/filemap.c:552 [inline]
 filemap_fdatawait include/linux/fs.h:2736 [inline]
 filemap_write_and_wait mm/filemap.c:647 [inline]
 filemap_write_and_wait+0xdb/0x150 mm/filemap.c:634
 ext4_ioctl_setflags+0x635/0x6e0 fs/ext4/ioctl.c:368
 ext4_ioctl+0x28af/0x3130 fs/ext4/ioctl.c:863
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0x991/0xc60 fs/ioctl.c:696
 ksys_ioctl+0xbd/0xe0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:718
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7840 Comm: syz-executor.5 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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