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BUG: KCSAN: data-race in wb_timer_fn / wbt_issue

write to 0xffff8881039ec304 of 4 bytes by interrupt on cpu 0:
 calc_wb_limits block/blk-wbt.c:304 [inline]
 scale_up block/blk-wbt.c:313 [inline]
 wb_timer_fn+0x403/0xa00 block/blk-wbt.c:382
 blk_stat_timer_fn+0x3f4/0x410 block/blk-stat.c:99
 call_timer_fn+0x2e/0x240 kernel/time/timer.c:1410
 expire_timers+0x116/0x260 kernel/time/timer.c:1455
 __run_timers+0x338/0x3d0 kernel/time/timer.c:1747
 run_timer_softirq+0x19/0x30 kernel/time/timer.c:1760
 __do_softirq+0x12c/0x2b1 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+0x32/0x40 arch/x86/kernel/irq_64.c:77
 invoke_softirq kernel/softirq.c:393 [inline]
 __irq_exit_rcu+0xb2/0xc0 kernel/softirq.c:423
 sysvec_apic_timer_interrupt+0x74/0x90 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:631
 native_safe_halt arch/x86/include/asm/irqflags.h:60 [inline]
 arch_safe_halt arch/x86/include/asm/irqflags.h:103 [inline]
 acpi_safe_halt drivers/acpi/processor_idle.c:111 [inline]
 acpi_idle_do_entry drivers/acpi/processor_idle.c:517 [inline]
 acpi_idle_enter+0x25b/0x2e0 drivers/acpi/processor_idle.c:648
 cpuidle_enter_state+0x2bd/0x750 drivers/cpuidle/cpuidle.c:237
 cpuidle_enter+0x3c/0x60 drivers/cpuidle/cpuidle.c:351
 call_cpuidle kernel/sched/idle.c:132 [inline]
 cpuidle_idle_call kernel/sched/idle.c:213 [inline]
 do_idle+0x193/0x230 kernel/sched/idle.c:273
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:369
 rest_init+0xd7/0xe0 init/main.c:721
 arch_call_rest_init+0xa/0xb
 start_kernel+0x5a0/0x625 init/main.c:1061
 secondary_startup_64_no_verify+0xb0/0xbb

read to 0xffff8881039ec304 of 4 bytes by task 26254 on cpu 1:
 rwb_enabled block/blk-wbt.c:80 [inline]
 wbt_issue+0x20/0xd0 block/blk-wbt.c:599
 __rq_qos_issue+0x3b/0x70 block/blk-rq-qos.c:54
 rq_qos_issue block/blk-rq-qos.h:159 [inline]
 blk_mq_start_request+0xc2/0x220 block/blk-mq.c:740
 scsi_queue_rq+0x105c/0x1380 drivers/scsi/scsi_lib.c:1684
 blk_mq_dispatch_rq_list+0x4cc/0xd30 block/blk-mq.c:1388
 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:186 [inline]
 blk_mq_do_dispatch_sched+0x370/0x610 block/blk-mq-sched.c:199
 __blk_mq_sched_dispatch_requests+0x1fd/0x2a0 block/blk-mq-sched.c:310
 blk_mq_sched_dispatch_requests+0x8f/0xf0 block/blk-mq-sched.c:341
 __blk_mq_run_hw_queue+0xee/0x1c0 block/blk-mq.c:1532
 __blk_mq_delay_run_hw_queue+0x17d/0x330 block/blk-mq.c:1609
 blk_mq_run_hw_queue+0x231/0x260 block/blk-mq.c:1662
 blk_mq_sched_insert_requests+0x144/0x210 block/blk-mq-sched.c:501
 blk_mq_flush_plug_list+0x2f5/0x400 block/blk-mq.c:1932
 blk_flush_plug_list+0x235/0x260 block/blk-core.c:1760
 blk_mq_submit_bio+0x81a/0x1020 block/blk-mq.c:2225
 __submit_bio_noacct_mq block/blk-core.c:1026 [inline]
 submit_bio_noacct+0x77d/0x930 block/blk-core.c:1059
 submit_bio+0x1f3/0x360 block/blk-core.c:1129
 ext4_io_submit fs/ext4/page-io.c:382 [inline]
 io_submit_add_bh fs/ext4/page-io.c:425 [inline]
 ext4_bio_write_page+0x958/0xda0 fs/ext4/page-io.c:552
 mpage_submit_page fs/ext4/inode.c:2092 [inline]
 mpage_map_and_submit_buffers fs/ext4/inode.c:2340 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2479 [inline]
 ext4_writepages+0xe9b/0x1e30 fs/ext4/inode.c:2792
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19d/0x1d0 mm/filemap.c:422
 __filemap_fdatawrite mm/filemap.c:430 [inline]
 filemap_flush+0x1f/0x30 mm/filemap.c:457
 ext4_alloc_da_blocks+0x4a/0x100 fs/ext4/inode.c:3156
 ext4_release_file+0x5b/0x1d0 fs/ext4/file.c:142
 __fput+0x243/0x4d0 fs/file_table.c:281
 ____fput+0x11/0x20 fs/file_table.c:314
 task_work_run+0x8e/0x110 kernel/task_work.c:151
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:164 [inline]
 exit_to_user_mode_prepare+0x13c/0x170 kernel/entry/common.c:191
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:266
 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: 1 PID: 26254 Comm: syz-executor.3 Not tainted 5.10.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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