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BUG: KCSAN: data-race in ext4_writepages / xas_clear_mark

write to 0xffff888119ba0c6c of 4 bytes by task 23862 on cpu 0:
 xa_mark_clear lib/xarray.c:75 [inline]
 xas_clear_mark+0x15a/0x170 lib/xarray.c:918
 __test_set_page_writeback+0x396/0x480 mm/page-writeback.c:2808
 ext4_bio_write_page+0xed/0xda0 fs/ext4/page-io.c:453
 mpage_submit_page fs/ext4/inode.c:2082 [inline]
 mpage_process_page_bufs+0x4f5/0x600 fs/ext4/inode.c:2196
 mpage_prepare_extent_to_map+0x4ec/0x650 fs/ext4/inode.c:2608
 ext4_writepages+0x682/0x1ef0 fs/ext4/inode.c:2736
 do_writepages+0x7b/0x150 mm/page-writeback.c:2354
 __filemap_fdatawrite_range+0x19b/0x1d0 mm/filemap.c:421
 file_write_and_wait_range+0x9f/0x120 mm/filemap.c:760
 ext4_sync_file+0xfc/0x6e0 fs/ext4/fsync.c:151
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2730 [inline]
 ext4_buffered_write_iter+0x369/0x3b0 fs/ext4/file.c:277
 ext4_file_write_iter+0x771/0x1010 include/linux/fs.h:774
 call_write_iter include/linux/fs.h:1868 [inline]
 do_iter_readv_writev+0x32e/0x3d0 fs/read_write.c:713
 do_iter_write+0x10e/0x470 fs/read_write.c:1018
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1059
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x562/0xb10 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1601 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888119ba0c6c of 4 bytes by task 23857 on cpu 1:
 xa_marked include/linux/xarray.h:416 [inline]
 mapping_tagged include/linux/fs.h:493 [inline]
 ext4_writepages+0x164/0x1ef0 fs/ext4/inode.c:2650
 do_writepages+0x7b/0x150 mm/page-writeback.c:2354
 __filemap_fdatawrite_range+0x19b/0x1d0 mm/filemap.c:421
 filemap_write_and_wait_range+0x8b/0x2a0 mm/filemap.c:654
 iomap_dio_rw+0x399/0x8c0 fs/iomap/direct-io.c:474
 ext4_dio_write_iter fs/ext4/file.c:545 [inline]
 ext4_file_write_iter+0xda6/0x1010 fs/ext4/file.c:653
 call_write_iter include/linux/fs.h:1868 [inline]
 do_iter_readv_writev+0x32e/0x3d0 fs/read_write.c:713
 do_iter_write+0x10e/0x470 fs/read_write.c:1018
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1059
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x562/0xb10 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1601 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 23857 Comm: syz-executor.1 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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