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BUG: KCSAN: data-race in wb_timer_fn / wbt_track

write to 0xffff888101010804 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+0x42a/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:1431
 expire_timers+0x116/0x260 kernel/time/timer.c:1476
 __run_timers+0x358/0x3f0 kernel/time/timer.c:1745
 run_timer_softirq+0x19/0x30 kernel/time/timer.c:1758
 __do_softirq+0x13c/0x2c3 kernel/softirq.c:345
 invoke_softirq kernel/softirq.c:221 [inline]
 __irq_exit_rcu+0xb4/0xc0 kernel/softirq.c:422
 sysvec_apic_timer_interrupt+0x6e/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632
 check_kcov_mode kernel/kcov.c:165 [inline]
 write_comp_data kernel/kcov.c:218 [inline]
 __sanitizer_cov_trace_const_cmp8+0x31/0x90 kernel/kcov.c:291
 constant_test_bit arch/x86/include/asm/bitops.h:207 [inline]
 test_bit include/asm-generic/bitops/instrumented-non-atomic.h:135 [inline]
 PageCompound include/linux/page-flags.h:198 [inline]
 page_mapcount include/linux/mm.h:853 [inline]
 zap_pte_range+0x5d4/0x13f0 mm/memory.c:1271
 zap_pmd_range mm/memory.c:1374 [inline]
 zap_pud_range mm/memory.c:1403 [inline]
 zap_p4d_range mm/memory.c:1424 [inline]
 unmap_page_range+0x540/0x650 mm/memory.c:1445
 unmap_single_vma+0x157/0x210 mm/memory.c:1490
 unmap_vmas+0xc0/0x170 mm/memory.c:1522
 exit_mmap+0x1be/0x400 mm/mmap.c:3218
 __mmput+0xa2/0x220 kernel/fork.c:1090
 mmput+0x3d/0x50 kernel/fork.c:1111
 exit_mm+0x344/0x430 kernel/exit.c:501
 do_exit+0x3fc/0x15e0 kernel/exit.c:812
 do_group_exit+0x17d/0x180 kernel/exit.c:922
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:933
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:931
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:931
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888101010804 of 4 bytes by task 14294 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+0x2e8/0x1060 block/blk-mq.c:2200
 __submit_bio_noacct_mq block/blk-core.c:1014 [inline]
 submit_bio_noacct+0x7c2/0x9a0 block/blk-core.c:1047
 submit_bio+0x200/0x370 block/blk-core.c:1118
 submit_bh_wbc+0x36b/0x3b0 fs/buffer.c:3055
 __block_write_full_page+0x648/0xa10 fs/buffer.c:1810
 block_write_full_page+0x260/0x290 fs/buffer.c:2981
 fat_writepage+0x20/0x30 fs/fat/inode.c:199
 writeout mm/migrate.c:896 [inline]
 fallback_migrate_page mm/migrate.c:920 [inline]
 move_to_new_page+0x305/0x6c0 mm/migrate.c:971
 __unmap_and_move+0x437/0x6a0 mm/migrate.c:1133
 unmap_and_move+0x131/0x690 mm/migrate.c:1200
 migrate_pages+0x2f7/0xfb0 mm/migrate.c:1472
 do_mbind+0xe47/0x1030 mm/mempolicy.c:1357
 kernel_mbind mm/mempolicy.c:1478 [inline]
 __do_sys_mbind mm/mempolicy.c:1485 [inline]
 __se_sys_mbind mm/mempolicy.c:1481 [inline]
 __x64_sys_mbind+0x142/0x170 mm/mempolicy.c:1481
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 14294 Comm: syz-executor.4 Not tainted 5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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