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BUG: KCSAN: data-race in writeback_sb_inodes / xas_set_mark

write to 0xffff88812b4282d4 of 4 bytes by task 9993 on cpu 1:
 xa_mark_set lib/xarray.c:68 [inline]
 xas_set_mark lib/xarray.c:885 [inline]
 xas_set_mark+0x14d/0x160 lib/xarray.c:869
 __xa_set_mark+0xd3/0x100 lib/xarray.c:1695
 __set_page_dirty+0x152/0x270 fs/buffer.c:584
 mark_buffer_dirty+0x27f/0x2c0 fs/buffer.c:1112
 __ext4_handle_dirty_metadata+0x284/0x350 fs/ext4/ext4_jbd2.c:298
 ext4_do_update_inode fs/ext4/inode.c:5334 [inline]
 ext4_mark_iloc_dirty+0xdb3/0x1580 fs/ext4/inode.c:5876
 ext4_mark_inode_dirty+0xe9/0x420 fs/ext4/inode.c:6055
 ext4_dirty_inode+0x86/0xb0 fs/ext4/inode.c:6086
 __mark_inode_dirty+0x5d4/0x940 fs/fs-writeback.c:2255
 generic_update_time+0x184/0x270 fs/inode.c:1667
 update_time fs/inode.c:1683 [inline]
 file_update_time+0x237/0x300 fs/inode.c:1898
 ext4_page_mkwrite+0xf9/0xce0 fs/ext4/inode.c:6204
 do_page_mkwrite+0x100/0x210 mm/memory.c:2208
 do_shared_fault mm/memory.c:3554 [inline]
 do_fault mm/memory.c:3622 [inline]
 handle_pte_fault mm/memory.c:3849 [inline]
 __handle_mm_fault+0x2089/0x2c70 mm/memory.c:3973
 handle_mm_fault+0x21b/0x530 mm/memory.c:4010
 do_user_addr_fault arch/x86/mm/fault.c:1441 [inline]
 __do_page_fault+0x3fb/0x9e0 arch/x86/mm/fault.c:1506
 do_page_fault+0x54/0x233 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202

read to 0xffff88812b4282d4 of 4 bytes by task 2639 on cpu 0:
 mapping_tagged include/linux/fs.h:521 [inline]
 requeue_inode fs/fs-writeback.c:1398 [inline]
 writeback_sb_inodes+0x6e3/0xa50 fs/fs-writeback.c:1740
 __writeback_inodes_wb+0xe8/0x1b0 fs/fs-writeback.c:1782
 wb_writeback+0x557/0x6a0 fs/fs-writeback.c:1891
 wb_check_old_data_flush fs/fs-writeback.c:1993 [inline]
 wb_do_writeback fs/fs-writeback.c:2046 [inline]
 wb_workfn+0x7bb/0x970 fs/fs-writeback.c:2075
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 2639 Comm: kworker/u4:4 Not tainted 5.4.0-rc6+ #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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