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BUG: KCSAN: data-race in __filemap_fdatawrite_range / __xa_clear_mark

write to 0xffff8881344b3924 of 4 bytes by interrupt on cpu 1:
 xa_mark_clear lib/xarray.c:75 [inline]
 xas_clear_mark lib/xarray.c:921 [inline]
 __xa_clear_mark+0x1c4/0x1e0 lib/xarray.c:1917
 test_clear_page_writeback+0x321/0x530 mm/page-writeback.c:2739
 end_page_writeback+0xd7/0x260 mm/filemap.c:1460
 ext4_finish_bio+0x429/0x480 fs/ext4/page-io.c:143
 ext4_end_bio+0x1ba/0x310 fs/ext4/page-io.c:364
 bio_endio+0x2d6/0x3a0 block/bio.c:1451
 req_bio_endio block/blk-core.c:265 [inline]
 blk_update_request+0x4f5/0xb40 block/blk-core.c:1456
 blk_mq_end_request+0x22/0x50 block/blk-mq.c:564
 lo_complete_rq+0xca/0x180 drivers/block/loop.c:497
 blk_complete_reqs block/blk-mq.c:576 [inline]
 blk_done_softirq+0x69/0x90 block/blk-mq.c:581
 __do_softirq+0x13c/0x2c3 kernel/softirq.c:345
 run_ksoftirqd+0x13/0x20 kernel/softirq.c:652
 smpboot_thread_fn+0x34f/0x520 kernel/smpboot.c:165
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881344b3924 of 4 bytes by task 27944 on cpu 0:
 xa_marked include/linux/xarray.h:418 [inline]
 mapping_tagged include/linux/fs.h:490 [inline]
 __filemap_fdatawrite_range+0x11c/0x1d0 mm/filemap.c:420
 file_write_and_wait_range+0x9f/0x120 mm/filemap.c:763
 ext4_sync_file+0x105/0x6e0 fs/ext4/fsync.c:151
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2843 [inline]
 ext4_buffered_write_iter+0x38f/0x3e0 fs/ext4/file.c:277
 ext4_file_write_iter+0x48a/0x10b0 fs/ext4/file.c:502
 call_write_iter include/linux/fs.h:1977 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x40a/0x750 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x7a6/0xe20 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27944 Comm: syz-executor.1 Tainted: G        W         5.12.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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