==================================================================
BUG: KCSAN: data-race in fprop_fraction_percpu / percpu_counter_add_batch

read to 0xffff8881299311c0 of 8 bytes by task 219 on cpu 0:
 fprop_fraction_percpu+0x8b/0x1c0 lib/flex_proportions.c:237
 __wb_calc_thresh+0x6f/0x250 mm/page-writeback.c:775
 wb_calc_thresh+0x96/0xc0 mm/page-writeback.c:795
 wb_over_bg_thresh+0x287/0x490 mm/page-writeback.c:1949
 wb_check_background_flush fs/fs-writeback.c:1952 [inline]
 wb_do_writeback fs/fs-writeback.c:2050 [inline]
 wb_workfn+0x3b3/0x970 fs/fs-writeback.c:2078
 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

write to 0xffff8881299311c0 of 8 bytes by interrupt on cpu 1:
 percpu_counter_add_batch+0xca/0x150 lib/percpu_counter.c:91
 __fprop_inc_percpu_max+0x9a/0x150 lib/flex_proportions.c:271
 wb_domain_writeout_inc mm/page-writeback.c:581 [inline]
 __wb_writeout_inc mm/page-writeback.c:605 [inline]
 test_clear_page_writeback+0x543/0x790 mm/page-writeback.c:2737
 end_page_writeback+0x9e/0x190 mm/filemap.c:1339
 end_buffer_async_write+0x2dc/0x3a0 fs/buffer.c:349
 end_bio_bh_io_sync+0x87/0xb0 fs/buffer.c:2978
 bio_endio+0x3a8/0x4f0 block/bio.c:1818
 req_bio_endio block/blk-core.c:242 [inline]
 blk_update_request+0x427/0x7b0 block/blk-core.c:1462
 scsi_end_request+0x6b/0x3e0 drivers/scsi/scsi_lib.c:579
 scsi_io_completion+0x11d/0xc80 drivers/scsi/scsi_lib.c:963
 scsi_finish_command+0x280/0x380 drivers/scsi/scsi.c:228
 scsi_softirq_done+0x259/0x280 drivers/scsi/scsi_lib.c:1477
 blk_done_softirq+0x1eb/0x250 block/blk-softirq.c:37
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 do_IRQ+0x81/0x130 arch/x86/kernel/irq.c:263
 ret_from_intr+0x0/0x19
 arch_local_irq_restore arch/x86/include/asm/paravirt.h:756 [inline]
 kcsan_setup_watchpoint+0x1d4/0x460 kernel/kcsan/core.c:436
 check_access kernel/kcsan/core.c:466 [inline]
 __tsan_read1 kernel/kcsan/core.c:593 [inline]
 __tsan_read1+0xc2/0x100 kernel/kcsan/core.c:593
 xas_reload include/linux/xarray.h:1492 [inline]
 filemap_map_pages+0x272/0x990 mm/filemap.c:2650
 do_fault_around mm/memory.c:3450 [inline]
 do_read_fault mm/memory.c:3484 [inline]
 do_fault mm/memory.c:3618 [inline]
 handle_pte_fault mm/memory.c:3849 [inline]
 __handle_mm_fault+0x2544/0x2c70 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+0x456/0x8d0 arch/x86/mm/fault.c:1506
 do_page_fault+0x38/0x194 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1202

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 27401 Comm: blkid Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================