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BUG: KCSAN: data-race in wb_timer_fn / wbt_inflight_cb

write to 0xffff888129e85304 of 4 bytes by interrupt on cpu 1:
 calc_wb_limits block/blk-wbt.c:304 [inline]
 scale_up block/blk-wbt.c:313 [inline]
 wb_timer_fn+0x42d/0xa40 block/blk-wbt.c:382
 blk_stat_timer_fn+0x3f4/0x410 block/blk-stat.c:99
 call_timer_fn+0x30/0x2a0 kernel/time/timer.c:1413
 expire_timers+0x116/0x290 kernel/time/timer.c:1458
 __run_timers+0x348/0x3e0 kernel/time/timer.c:1755
 run_timer_softirq+0x2e/0x60 kernel/time/timer.c:1768
 __do_softirq+0x198/0x360 kernel/softirq.c:298
 asm_call_irq_on_stack+0xf/0x20
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline]
 do_softirq_own_stack+0x5b/0x70 arch/x86/kernel/irq_64.c:77
 invoke_softirq kernel/softirq.c:393 [inline]
 __irq_exit_rcu+0x115/0x120 kernel/softirq.c:423
 sysvec_apic_timer_interrupt+0xba/0xd0 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:581
 preempt_count arch/x86/include/asm/preempt.h:26 [inline]
 check_kcov_mode kernel/kcov.c:163 [inline]
 write_comp_data kernel/kcov.c:218 [inline]
 __sanitizer_cov_trace_cmp4+0x14/0xa0 kernel/kcov.c:258
 __tlb_remove_page_size+0x72/0x180 mm/mmu_gather.c:82
 __tlb_remove_page include/asm-generic/tlb.h:438 [inline]
 zap_pte_range+0x751/0x1630 mm/memory.c:1285
 zap_pmd_range mm/memory.c:1386 [inline]
 zap_pud_range mm/memory.c:1415 [inline]
 zap_p4d_range mm/memory.c:1436 [inline]
 unmap_page_range+0x751/0x870 mm/memory.c:1457
 unmap_single_vma+0x157/0x210 mm/memory.c:1502
 unmap_vmas+0xc0/0x150 mm/memory.c:1534
 exit_mmap+0x1c7/0x3b0 mm/mmap.c:3183
 __mmput+0xa2/0x220 kernel/fork.c:1077
 mmput+0x38/0x40 kernel/fork.c:1098
 exit_mm+0x2c8/0x330 kernel/exit.c:483
 do_exit+0x40f/0x16c0 kernel/exit.c:793
 do_group_exit+0x17a/0x180 kernel/exit.c:903
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:914
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:912
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:912
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888129e85304 of 4 bytes by task 27500 on cpu 0:
 rwb_enabled block/blk-wbt.c:80 [inline]
 get_limit block/blk-wbt.c:458 [inline]
 wbt_inflight_cb+0x3f/0x220 block/blk-wbt.c:495
 rq_qos_wait+0xac/0x220 block/blk-rq-qos.c:266
 __wbt_wait block/blk-wbt.c:518 [inline]
 wbt_wait+0x1bb/0x2b0 block/blk-wbt.c:583
 __rq_qos_throttle+0x39/0x70 block/blk-rq-qos.c:72
 rq_qos_throttle block/blk-rq-qos.h:182 [inline]
 blk_mq_submit_bio+0x244/0x1130 block/blk-mq.c:2168
 __submit_bio_noacct_mq block/blk-core.c:1180 [inline]
 submit_bio_noacct+0x772/0x950 block/blk-core.c:1213
 submit_bio+0x200/0x370 block/blk-core.c:1283
 ext4_io_submit+0xcd/0xf0 fs/ext4/page-io.c:382
 ext4_writepages+0x143a/0x1ed0 fs/ext4/inode.c:2801
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19b/0x1d0 mm/filemap.c:422
 __filemap_fdatawrite mm/filemap.c:430 [inline]
 filemap_flush+0x1f/0x30 mm/filemap.c:457
 ext4_alloc_da_blocks+0x4c/0x130 fs/ext4/inode.c:3145
 ext4_release_file+0x5b/0x1c0 fs/ext4/file.c:142
 __fput+0x246/0x4d0 fs/file_table.c:281
 ____fput+0x11/0x20 fs/file_table.c:314
 task_work_run+0x8e/0x110 kernel/task_work.c:141
 get_signal+0x11cf/0x1650 kernel/signal.c:2561
 arch_do_signal+0x25/0x270 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
 exit_to_user_mode_prepare+0x124/0x210 kernel/entry/common.c:192
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:267
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27500 Comm: syz-executor.4 Not tainted 5.9.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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