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

write to 0xffff888129d42304 of 4 bytes by interrupt on cpu 0:
 calc_wb_limits.part.0+0x70/0xa0 block/blk-wbt.c:304
 calc_wb_limits block/blk-wbt.c:298 [inline]
 scale_up block/blk-wbt.c:313 [inline]
 scale_up+0x7d/0x250 block/blk-wbt.c:309
 wb_timer_fn+0x2d6/0xad0 block/blk-wbt.c:382
 blk_stat_timer_fn+0x3af/0x3d0 block/blk-stat.c:99
 call_timer_fn+0x58/0x2e0 kernel/time/timer.c:1405
 expire_timers kernel/time/timer.c:1450 [inline]
 __run_timers kernel/time/timer.c:1774 [inline]
 __run_timers kernel/time/timer.c:1741 [inline]
 run_timer_softirq+0xb14/0xbd0 kernel/time/timer.c:1787
 __do_softirq+0x118/0x34a kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xb5/0xd0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:546 [inline]
 smp_apic_timer_interrupt+0xe2/0x270 arch/x86/kernel/apic/apic.c:1140
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 arch_local_irq_restore arch/x86/include/asm/paravirt.h:759 [inline]
 kcsan_setup_watchpoint+0x25a/0x440 kernel/kcsan/core.c:542
 pte_val arch/x86/include/asm/paravirt.h:385 [inline]
 pte_pfn arch/x86/include/asm/pgtable.h:215 [inline]
 vm_normal_page+0x2c/0x220 mm/memory.c:595
 do_wp_page+0xee/0xca0 mm/memory.c:2906
 handle_pte_fault mm/memory.c:4231 [inline]
 __handle_mm_fault+0x2d96/0x2da0 mm/memory.c:4345
 handle_mm_fault+0x21c/0x540 mm/memory.c:4382
 do_user_addr_fault arch/x86/mm/fault.c:1464 [inline]
 do_page_fault+0x48a/0xa96 arch/x86/mm/fault.c:1535
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203

read to 0xffff888129d42304 of 4 bytes by task 1934 on cpu 1:
 rwb_enabled block/blk-wbt.c:80 [inline]
 get_limit block/blk-wbt.c:466 [inline]
 wbt_inflight_cb+0x47/0x220 block/blk-wbt.c:503
 rq_qos_wait+0x26b/0x300 block/blk-rq-qos.c:266
 __wbt_wait block/blk-wbt.c:526 [inline]
 wbt_wait+0x15f/0x260 block/blk-wbt.c:591
 __rq_qos_throttle+0x42/0x70 block/blk-rq-qos.c:72
 rq_qos_throttle block/blk-rq-qos.h:182 [inline]
 blk_mq_make_request+0x297/0xf60 block/blk-mq.c:1998
 generic_make_request block/blk-core.c:1075 [inline]
 generic_make_request+0x196/0x700 block/blk-core.c:1017
 submit_bio+0x8f/0x3a0 block/blk-core.c:1200
 ext4_io_submit+0xdf/0x110 fs/ext4/page-io.c:382
 ext4_writepages+0xd96/0x1e10 fs/ext4/inode.c:2800
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __filemap_fdatawrite_range+0x1bb/0x220 mm/filemap.c:421
 __filemap_fdatawrite mm/filemap.c:429 [inline]
 filemap_flush+0x2a/0x40 mm/filemap.c:456
 collapse_file+0x27ca/0x27e0 mm/khugepaged.c:1639
 khugepaged_scan_file mm/khugepaged.c:1920 [inline]
 khugepaged_scan_mm_slot mm/khugepaged.c:2016 [inline]
 khugepaged_do_scan mm/khugepaged.c:2100 [inline]
 khugepaged+0x1e1d/0x2850 mm/khugepaged.c:2145
 kthread+0x203/0x230 kernel/kthread.c:268
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1934 Comm: khugepaged Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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