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

write to 0xffff88812923af04 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:326 [inline]
 scale_down.part.0+0xcb/0x230 block/blk-wbt.c:323
 scale_down block/blk-wbt.c:321 [inline]
 wb_timer_fn+0x6fb/0xad0 block/blk-wbt.c:395
 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]
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
 _raw_spin_unlock_irqrestore+0x4d/0x80 kernel/locking/spinlock.c:191
 spin_unlock_irqrestore include/linux/spinlock.h:408 [inline]
 pcpu_alloc+0x38e/0xd00 mm/percpu.c:1672
 __alloc_percpu+0x2a/0x40 mm/percpu.c:1767
 xt_percpu_counter_alloc+0xfb/0x120 net/netfilter/x_tables.c:1842
 find_check_entry.isra.0+0x63/0x580 net/ipv6/netfilter/ip6_tables.c:546
 translate_table+0x76d/0xc10 net/ipv6/netfilter/ip6_tables.c:734
 do_replace net/ipv6/netfilter/ip6_tables.c:1153 [inline]
 do_ip6t_set_ctl+0x21d/0x333 net/ipv6/netfilter/ip6_tables.c:1681
 nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
 nf_setsockopt+0x67/0xa0 net/netfilter/nf_sockopt.c:115
 ipv6_setsockopt net/ipv6/ipv6_sockglue.c:955 [inline]
 ipv6_setsockopt+0x118/0x130 net/ipv6/ipv6_sockglue.c:939
 tcp_setsockopt net/ipv4/tcp.c:3167 [inline]
 tcp_setsockopt+0x6c/0xb0 net/ipv4/tcp.c:3161
 sock_common_setsockopt+0x5d/0x80 net/core/sock.c:3172
 __sys_setsockopt+0x1d6/0x380 net/socket.c:2132
 __do_sys_setsockopt net/socket.c:2148 [inline]
 __se_sys_setsockopt net/socket.c:2145 [inline]
 __x64_sys_setsockopt+0x6b/0x80 net/socket.c:2145
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812923af04 of 4 bytes by task 28 on cpu 1:
 rwb_enabled block/blk-wbt.c:80 [inline]
 bio_to_wbt_flags block/blk-wbt.c:551 [inline]
 wbt_wait+0x4d/0x260 block/blk-wbt.c:584
 __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
 io_submit_add_bh fs/ext4/page-io.c:423 [inline]
 ext4_bio_write_page+0x4ba/0xba5 fs/ext4/page-io.c:550
 mpage_submit_page+0xd5/0x190 fs/ext4/inode.c:2073
 mpage_process_page_bufs+0x3df/0x400 fs/ext4/inode.c:2187
 mpage_prepare_extent_to_map+0x43b/0x6e0 fs/ext4/inode.c:2595
 ext4_writepages+0x5a1/0x1e10 fs/ext4/inode.c:2723
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __writeback_single_inode+0xaa/0x910 fs/fs-writeback.c:1452
 writeback_sb_inodes+0x4c8/0xa10 fs/fs-writeback.c:1716
 wb_writeback+0x1f9/0x6a0 fs/fs-writeback.c:1892
 wb_do_writeback fs/fs-writeback.c:2037 [inline]
 wb_workfn+0x215/0x970 fs/fs-writeback.c:2078
 process_one_work+0x424/0x930 kernel/workqueue.c:2268
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2414
 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: 28 Comm: kworker/u4:2 Not tainted 5.7.0-rc1-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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