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BUG: KCSAN: data-race in wb_timer_fn / wbt_track

write to 0xffff888128e5e704 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+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_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:706
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
 do_softirq_own_stack+0x5d/0x80 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

read to 0xffff888128e5e704 of 4 bytes by task 8715 on cpu 1:
 rwb_enabled block/blk-wbt.c:80 [inline]
 bio_to_wbt_flags block/blk-wbt.c:543 [inline]
 wbt_track+0x23/0x130 block/blk-wbt.c:592
 __rq_qos_track+0x50/0x90 block/blk-rq-qos.c:81
 rq_qos_track block/blk-rq-qos.h:189 [inline]
 blk_mq_submit_bio+0x2d0/0x1130 block/blk-mq.c:2170
 __submit_bio_noacct_mq block/blk-core.c:1179 [inline]
 submit_bio_noacct+0x772/0x950 block/blk-core.c:1212
 submit_bio+0x200/0x370 block/blk-core.c:1282
 submit_bio_wait+0x88/0x120 block/bio.c:1151
 blkdev_issue_flush+0xd3/0xf0 block/blk-flush.c:444
 ext4_sync_file+0x3eb/0x6e0 fs/ext4/fsync.c:177
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2744 [inline]
 ext4_buffered_write_iter+0x369/0x3b0 fs/ext4/file.c:277
 ext4_file_write_iter+0x57b/0x1000 fs/ext4/file.c:498
 call_write_iter include/linux/fs.h:1882 [inline]
 do_iter_readv_writev+0x32e/0x3d0 fs/read_write.c:713
 do_iter_write+0x112/0x4b0 fs/read_write.c:1018
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1059
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x56a/0xba0 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1595 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1587
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8715 Comm: syz-executor.5 Not tainted 5.9.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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