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BUG: KCSAN: data-race in __writeback_single_inode / xas_set_mark

write to 0xffff88812b403914 of 4 bytes by task 24056 on cpu 1:
 xa_mark_set lib/xarray.c:68 [inline]
 xas_set_mark lib/xarray.c:885 [inline]
 xas_set_mark+0x17d/0x1a0 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
 mark_inode_dirty include/linux/fs.h:2165 [inline]
 generic_write_end+0x1b7/0x1f0 fs/buffer.c:2159
 ext4_da_write_end+0x158/0x620 fs/ext4/inode.c:3189
 generic_perform_write+0x1d3/0x320 mm/filemap.c:3315
 __generic_file_write_iter+0x251/0x380 mm/filemap.c:3433
 ext4_file_write_iter+0x1bd/0xa00 fs/ext4/file.c:268

read to 0xffff88812b403914 of 4 bytes by task 2640 on cpu 0:
 mapping_tagged include/linux/fs.h:521 [inline]
 __writeback_single_inode+0x367/0x8e0 fs/fs-writeback.c:1499
 writeback_sb_inodes+0x4ba/0xa50 fs/fs-writeback.c:1713
 __writeback_inodes_wb+0xe8/0x1b0 fs/fs-writeback.c:1782
 wb_writeback+0x557/0x6a0 fs/fs-writeback.c:1891
 wb_do_writeback fs/fs-writeback.c:2034 [inline]
 wb_workfn+0x22e/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: 2640 Comm: kworker/u4:4 Not tainted 5.4.0-rc3+ #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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