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

write to 0xffff88821aab7a04 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:1146
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 __read_once_size include/linux/compiler.h:232 [inline]
 check_kcov_mode kernel/kcov.c:155 [inline]
 write_comp_data+0x1e/0x70 kernel/kcov.c:208
 compound_head include/linux/page-flags.h:176 [inline]
 get_page include/linux/mm.h:995 [inline]
 copy_one_pte mm/memory.c:790 [inline]
 copy_pte_range mm/memory.c:841 [inline]
 copy_pmd_range mm/memory.c:892 [inline]
 copy_pud_range mm/memory.c:926 [inline]
 copy_p4d_range mm/memory.c:948 [inline]
 copy_page_range+0xb13/0x1a40 mm/memory.c:1010
 dup_mmap kernel/fork.c:610 [inline]
 dup_mm+0x72e/0xb90 kernel/fork.c:1366
 copy_mm kernel/fork.c:1422 [inline]
 copy_process+0x39ad/0x3b10 kernel/fork.c:2087
 _do_fork+0xf7/0x790 kernel/fork.c:2436
 __do_sys_clone kernel/fork.c:2591 [inline]
 __se_sys_clone kernel/fork.c:2572 [inline]
 __x64_sys_clone+0x12e/0x170 kernel/fork.c:2572
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88821aab7a04 of 4 bytes by task 3768 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:1984
 generic_make_request block/blk-core.c:1069 [inline]
 generic_make_request+0x196/0x700 block/blk-core.c:1011
 submit_bio+0x8f/0x3a0 block/blk-core.c:1195
 submit_bh_wbc+0x40d/0x460 fs/buffer.c:3112
 submit_bh fs/buffer.c:3118 [inline]
 __bread_slow fs/buffer.c:1217 [inline]
 __bread_gfp+0xe1/0x1d0 fs/buffer.c:1399
 sb_bread include/linux/buffer_head.h:307 [inline]
 fat__get_entry+0x379/0x510 fs/fat/dir.c:100
 fat_get_entry fs/fat/dir.c:128 [inline]
 fat_get_short_entry+0xd4/0x1d0 fs/fat/dir.c:877
 fat_subdirs+0x6a/0x110 fs/fat/dir.c:943
 fat_read_root fs/fat/inode.c:1417 [inline]
 fat_fill_super+0x1425/0x1da0 fs/fat/inode.c:1863
 vfat_fill_super+0x37/0x50 fs/fat/namei_vfat.c:1050
 mount_bdev+0x264/0x2d0 fs/super.c:1417
 vfat_mount+0x38/0x50 fs/fat/namei_vfat.c:1057
 legacy_get_tree+0x78/0xf0 fs/fs_context.c:622
 vfs_get_tree+0x52/0x190 fs/super.c:1547
 do_new_mount fs/namespace.c:2822 [inline]
 do_mount+0xff0/0x14d0 fs/namespace.c:3107
 __do_sys_mount fs/namespace.c:3316 [inline]
 __se_sys_mount fs/namespace.c:3293 [inline]
 __x64_sys_mount+0x12b/0x1a0 fs/namespace.c:3293
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3768 Comm: syz-executor.5 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================