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BUG: KCSAN: data-race in ext4_writepages / xas_clear_mark

read to 0xffff8880ba053d44 of 4 bytes by task 2640 on cpu 0:
 mapping_tagged include/linux/fs.h:521 [inline]
 ext4_writepages+0x1b4/0x2300 fs/ext4/inode.c:2736
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __writeback_single_inode+0xaf/0x8e0 fs/fs-writeback.c:1449
 writeback_sb_inodes+0x4ba/0xa50 fs/fs-writeback.c:1713
 wb_writeback+0x1f9/0x6a0 fs/fs-writeback.c:1889
 wb_do_writeback fs/fs-writeback.c:2034 [inline]
 wb_workfn+0x22e/0x970 fs/fs-writeback.c:2075
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

write to 0xffff8880ba053d44 of 4 bytes by interrupt on cpu 1:
 xa_mark_clear lib/xarray.c:74 [inline]
 xas_clear_mark lib/xarray.c:917 [inline]
 xas_clear_mark+0x1a0/0x1d0 lib/xarray.c:898
 __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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 14498 Comm: syz-executor.2 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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