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BUG: KCSAN: data-race in __xa_set_mark / writeback_sb_inodes

write to 0xffff8881415da63c of 4 bytes by task 8085 on cpu 0:
 xa_mark_set lib/xarray.c:69 [inline]
 xas_set_mark lib/xarray.c:889 [inline]
 __xa_set_mark+0x166/0x190 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:5134 [inline]
 ext4_mark_iloc_dirty+0x12ed/0x1650 fs/ext4/inode.c:5711
 __ext4_mark_inode_dirty+0x450/0x610 fs/ext4/inode.c:5905
 ext4_dirty_inode+0xa6/0xc0 fs/ext4/inode.c:5941
 __mark_inode_dirty+0x74/0x740 fs/fs-writeback.c:2260
 generic_update_time fs/inode.c:1764 [inline]
 update_time fs/inode.c:1777 [inline]
 file_update_time+0x3b0/0x3f0 fs/inode.c:1992
 file_modified+0x62/0x80 fs/inode.c:2015
 ext4_write_checks fs/ext4/file.c:248 [inline]
 ext4_buffered_write_iter+0x1f9/0x3d0 fs/ext4/file.c:265
 ext4_file_write_iter+0x45e/0x1090 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1887 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x617/0x690 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881415da63c of 4 bytes by task 9864 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_start_all fs/fs-writeback.c:2020 [inline]
 wb_do_writeback+0x3f9/0x5d0 fs/fs-writeback.c:2046
 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+0x1fa/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: 9864 Comm: kworker/u4:5 Not tainted 5.10.0-rc1-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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