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BUG: KCSAN: data-race in wb_timer_fn / wbt_inflight_cb

write to 0xffff888128f94604 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_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
 console_unlock+0x8ed/0xab0 arch/x86/include/asm/paravirt.h:770
 vprintk_emit+0x37f/0x4f0 kernel/printk/printk.c:2029
 vprintk_default+0x24/0x30 kernel/printk/printk.c:2047
 vprintk_func+0x13d/0x140 kernel/printk/printk_safe.c:393
 printk+0x62/0x82 kernel/printk/printk.c:2078
 fat_msg+0x80/0xaf fs/fat/misc.c:56
 fat_fill_super+0x2898/0x2a90 fs/fat/inode.c:1891
 msdos_fill_super+0x29/0x30 fs/fat/namei_msdos.c:653
 mount_bdev+0x1e8/0x290 fs/super.c:1417
 msdos_mount+0x2d/0x40 fs/fat/namei_msdos.c:660
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4d/0x1a0 fs/super.c:1547
 do_new_mount fs/namespace.c:2875 [inline]
 path_mount+0x118d/0x1c70 fs/namespace.c:3192
 do_mount fs/namespace.c:3205 [inline]
 __do_sys_mount fs/namespace.c:3413 [inline]
 __se_sys_mount+0x126/0x180 fs/namespace.c:3390
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3390
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888128f94604 of 4 bytes by task 22385 on cpu 0:
 get_limit block/blk-wbt.c:473 [inline]
 wbt_inflight_cb+0xc6/0x220 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+0x69c/0x1ef0 fs/ext4/inode.c:2739
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __writeback_single_inode+0x84/0x600 fs/fs-writeback.c:1461
 writeback_sb_inodes+0x6c0/0xff0 fs/fs-writeback.c:1721
 wb_writeback+0x28d/0x6f0 fs/fs-writeback.c:1894
 wb_do_writeback+0x101/0x5f0 fs/fs-writeback.c:2039
 wb_workfn+0xc8/0x470 fs/fs-writeback.c:2080
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 22385 Comm: kworker/u4:6 Not tainted 5.9.0-rc3-syzkaller #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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