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BUG: KCSAN: data-race in ext4_writepages / xas_clear_mark

write to 0xffff88801863dd04 of 4 bytes by task 907 on cpu 1:
 xa_mark_clear lib/xarray.c:75 [inline]
 xas_clear_mark+0x16c/0x180 lib/xarray.c:921
 __test_set_page_writeback+0x3db/0x4f0 mm/page-writeback.c:2802
 ext4_bio_write_page+0xfe/0xe60 fs/ext4/page-io.c:450
 mpage_submit_page fs/ext4/inode.c:2102 [inline]
 mpage_process_page_bufs+0x4db/0x5f0 fs/ext4/inode.c:2216
 mpage_prepare_extent_to_map+0x4e6/0x640 fs/ext4/inode.c:2628
 ext4_writepages+0x674/0x1e70 fs/ext4/inode.c:2756
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19d/0x1d0 mm/filemap.c:424
 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:1319 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1311
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88801863dd04 of 4 bytes by task 903 on cpu 0:
 xa_marked include/linux/xarray.h:418 [inline]
 mapping_tagged include/linux/fs.h:490 [inline]
 ext4_writepages+0x155/0x1e70 fs/ext4/inode.c:2670
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19d/0x1d0 mm/filemap.c:424
 filemap_write_and_wait_range+0x8b/0x2a0 mm/filemap.c:657
 __iomap_dio_rw+0x40a/0xa30 fs/iomap/direct-io.c:525
 iomap_dio_rw+0x30/0x70 fs/iomap/direct-io.c:641
 ext4_dio_write_iter fs/ext4/file.c:551 [inline]
 ext4_file_write_iter+0xe5d/0x10b0 fs/ext4/file.c:661
 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: 903 Comm: syz-executor.5 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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