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BUG: KCSAN: data-race in xas_find_marked / xas_set_mark

read to 0xffff8881259866a8 of 8 bytes by task 21 on cpu 1:
 xas_find_chunk include/linux/xarray.h:1590 [inline]
 xas_find_marked+0x17a/0x7b0 lib/xarray.c:1187
 find_get_pages_range_tag+0x111/0x670 mm/filemap.c:1924
 pagevec_lookup_range_tag+0x45/0x70 mm/swap.c:1054
 mpage_prepare_extent_to_map+0x1e2/0x760 fs/ext4/inode.c:2645
 ext4_writepages+0xb2b/0x2300 fs/ext4/inode.c:2866
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __writeback_single_inode+0xaf/0x8e0 fs/fs-writeback.c:1449
 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_check_background_flush fs/fs-writeback.c:1959 [inline]
 wb_do_writeback fs/fs-writeback.c:2047 [inline]
 wb_workfn+0x696/0x970 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

write to 0xffff8881259866a8 of 8 bytes by task 7854 on cpu 0:
 __test_and_set_bit include/asm-generic/bitops-instrumented.h:168 [inline]
 node_set_mark lib/xarray.c:92 [inline]
 xas_set_mark+0x122/0x1a0 lib/xarray.c:878
 __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
 __block_commit_write.isra.0+0x11f/0x170 fs/buffer.c:2041
 block_write_end+0x6d/0x140 fs/buffer.c:2119
 generic_write_end+0x8a/0x1f0 fs/buffer.c:2133
 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
 call_write_iter include/linux/fs.h:1895 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7854 Comm: syz-executor.3 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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