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BUG: KCSAN: data-race in writeback_sb_inodes / xas_clear_mark

write to 0xffff888014d9e304 of 4 bytes by task 17321 on cpu 0:
 xa_mark_clear lib/xarray.c:75 [inline]
 xas_clear_mark+0x16c/0x180 lib/xarray.c:921
 __test_set_page_writeback+0x3c3/0x4d0 mm/page-writeback.c:2800
 ext4_bio_write_page+0xfe/0xe70 fs/ext4/page-io.c:450
 mpage_submit_page fs/ext4/inode.c:2101 [inline]
 mpage_process_page_bufs+0x4db/0x5d0 fs/ext4/inode.c:2215
 mpage_prepare_extent_to_map+0x4d6/0x630 fs/ext4/inode.c:2627
 ext4_writepages+0x674/0x1e50 fs/ext4/inode.c:2755
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19d/0x1d0 mm/filemap.c:422
 file_write_and_wait_range+0x9f/0x120 mm/filemap.c:761
 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:2737 [inline]
 ext4_buffered_write_iter+0x384/0x3d0 fs/ext4/file.c:278
 ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1901 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4b0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x42a/0x780 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:933
 splice_direct_to_actor+0x345/0x650 fs/splice.c:888
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x5db/0xca0 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1318 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1304
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888014d9e304 of 4 bytes by task 8 on cpu 1:
 xa_marked include/linux/xarray.h:416 [inline]
 mapping_tagged include/linux/fs.h:488 [inline]
 requeue_inode fs/fs-writeback.c:1409 [inline]
 writeback_sb_inodes+0x91d/0x1020 fs/fs-writeback.c:1750
 wb_writeback+0x27d/0x660 fs/fs-writeback.c:1896
 wb_do_writeback+0x101/0x5d0 fs/fs-writeback.c:2041
 wb_workfn+0xb8/0x410 fs/fs-writeback.c:2082
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8 Comm: kworker/u4:0 Not tainted 5.11.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
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