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BUG: KCSAN: data-race in calc_wb_limits.part.0 / wbt_wait

write to 0xffff888128c69d04 of 4 bytes by interrupt on cpu 0:
 calc_wb_limits.part.0+0x7b/0xb0 block/blk-wbt.c:304
 calc_wb_limits block/blk-wbt.c:298 [inline]
 scale_up block/blk-wbt.c:313 [inline]
 scale_up+0x7f/0x250 block/blk-wbt.c:309
 wb_timer_fn+0x2cd/0xad0 block/blk-wbt.c:393
 blk_stat_timer_fn+0x3b0/0x3d0 block/blk-stat.c:98
 call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1773 [inline]
 __run_timers kernel/time/timer.c:1740 [inline]
 run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 run_ksoftirqd+0x46/0x60 kernel/softirq.c:603
 smpboot_thread_fn+0x37d/0x4a0 kernel/smpboot.c:165
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff888128c69d04 of 4 bytes by task 2637 on cpu 1:
 rwb_enabled block/blk-wbt.c:80 [inline]
 bio_to_wbt_flags block/blk-wbt.c:551 [inline]
 wbt_wait+0x52/0x250 block/blk-wbt.c:584
 __rq_qos_throttle+0x47/0x70 block/blk-rq-qos.c:72
 rq_qos_throttle block/blk-rq-qos.h:182 [inline]
 blk_mq_make_request+0x29c/0xf60 block/blk-mq.c:1971
 generic_make_request block/blk-core.c:1064 [inline]
 generic_make_request+0x196/0x740 block/blk-core.c:1006
 submit_bio+0x96/0x3c0 block/blk-core.c:1190
 ext4_io_submit+0xdf/0x110 fs/ext4/page-io.c:348
 ext4_writepages+0xea9/0x2300 fs/ext4/inode.c:2899
 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_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: 1 PID: 2637 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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