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BUG: KCSAN: data-race in __xa_set_mark / writeback_sb_inodes

write to 0xffff8881004772bc of 4 bytes by task 3239 on cpu 0:
 xa_mark_set lib/xarray.c:69 [inline]
 xas_set_mark lib/xarray.c:889 [inline]
 __xa_set_mark+0x187/0x1b0 lib/xarray.c:1898
 __set_page_dirty+0x17e/0x1d0 fs/buffer.c:609
 mark_buffer_dirty+0x126/0x230 fs/buffer.c:1137
 __ext4_handle_dirty_metadata+0x20a/0x590 fs/ext4/ext4_jbd2.c:362
 ext4_do_update_inode fs/ext4/inode.c:5135 [inline]
 ext4_mark_iloc_dirty+0x12ed/0x1650 fs/ext4/inode.c:5712
 __ext4_mark_inode_dirty+0x450/0x610 fs/ext4/inode.c:5906
 ext4_dirty_inode+0xa6/0xc0 fs/ext4/inode.c:5942
 __mark_inode_dirty+0x74/0x740 fs/fs-writeback.c:2260
 mark_inode_dirty_sync include/linux/fs.h:2188 [inline]
 dquot_free_space include/linux/quotaops.h:382 [inline]
 dquot_free_block include/linux/quotaops.h:392 [inline]
 ext4_free_blocks+0x1517/0x1c80 fs/ext4/mballoc.c:5493
 ext4_ext_try_to_merge_up fs/ext4/extents.c:1830 [inline]
 ext4_ext_try_to_merge+0x2fa/0x310 fs/ext4/extents.c:1857
 ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3721 [inline]
 ext4_ext_handle_unwritten_extents+0x64f/0xa90 fs/ext4/extents.c:3849
 ext4_ext_map_blocks+0x728/0x1fc0 fs/ext4/extents.c:4119
 ext4_map_blocks+0x700/0xfc0 fs/ext4/inode.c:628
 ext4_convert_unwritten_extents+0x15a/0x2c0 fs/ext4/extents.c:4760
 ext4_convert_unwritten_io_end_vec+0xa4/0x130 fs/ext4/extents.c:4799
 ext4_end_io_end fs/ext4/page-io.c:187 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:260 [inline]
 ext4_end_io_rsv_work+0x198/0x360 fs/ext4/page-io.c:274
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
 worker_thread+0x635/0xb90 kernel/workqueue.c:2418
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff8881004772bc of 4 bytes by task 20101 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:1748
 __writeback_inodes_wb+0xb0/0x2a0 fs/fs-writeback.c:1790
 wb_writeback+0x290/0x660 fs/fs-writeback.c:1896
 wb_check_old_data_flush fs/fs-writeback.c:1998 [inline]
 wb_do_writeback+0x520/0x5d0 fs/fs-writeback.c:2051
 wb_workfn+0xb8/0x410 fs/fs-writeback.c:2080
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
 worker_thread+0x635/0xb90 kernel/workqueue.c:2418
 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: 20101 Comm: kworker/u4:2 Not tainted 5.10.0-rc6-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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