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BUG: KCSAN: data-race in wb_timer_fn / wbt_track

write to 0xffff88810389c704 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+0x403/0xa00 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:1415
 expire_timers+0x116/0x260 kernel/time/timer.c:1460
 __run_timers+0x328/0x3c0 kernel/time/timer.c:1752
 run_timer_softirq+0x19/0x30 kernel/time/timer.c:1765
 __do_softirq+0x12c/0x2b1 kernel/softirq.c:298
 asm_call_irq_on_stack+0xf/0x20
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline]
 do_softirq_own_stack+0x32/0x40 arch/x86/kernel/irq_64.c:77
 invoke_softirq kernel/softirq.c:393 [inline]
 __irq_exit_rcu+0xb2/0xc0 kernel/softirq.c:423
 sysvec_apic_timer_interrupt+0x74/0x90 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:631
 native_restore_fl arch/x86/include/asm/irqflags.h:41 [inline]
 arch_local_irq_restore arch/x86/include/asm/irqflags.h:84 [inline]
 kcsan_setup_watchpoint+0x1ec/0x4d0 kernel/kcsan/core.c:591
 ext4_journal_blocks_per_page fs/ext4/ext4_jbd2.h:410 [inline]
 ext4_writepage_trans_blocks+0x45/0x200 fs/ext4/inode.c:5662
 ext4_truncate+0x494/0xbb0 fs/ext4/inode.c:4220
 ext4_evict_inode+0x8fa/0xbc0 fs/ext4/inode.c:280
 evict+0x19f/0x470 fs/inode.c:578
 iput_final fs/inode.c:1654 [inline]
 iput+0x421/0x510 fs/inode.c:1680
 dentry_unlink_inode+0x1f3/0x210 fs/dcache.c:374
 d_delete+0x70/0xa0 fs/dcache.c:2470
 vfs_rmdir+0x271/0x290 fs/namei.c:3727
 do_rmdir+0x16e/0x300 fs/namei.c:3774
 __do_sys_rmdir fs/namei.c:3792 [inline]
 __se_sys_rmdir fs/namei.c:3790 [inline]
 __x64_sys_rmdir+0x2c/0x30 fs/namei.c:3790
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810389c704 of 4 bytes by task 22000 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+0x2c0/0x1020 block/blk-mq.c:2187
 __submit_bio_noacct_mq block/blk-core.c:1026 [inline]
 submit_bio_noacct+0x77d/0x930 block/blk-core.c:1059
 submit_bio+0x1f3/0x360 block/blk-core.c:1129
 submit_bh_wbc+0x38c/0x3d0 fs/buffer.c:3054
 submit_bh fs/buffer.c:3060 [inline]
 __sync_dirty_buffer+0x12c/0x1d0 fs/buffer.c:3155
 sync_dirty_buffer+0x16/0x20 fs/buffer.c:3168
 __ext4_handle_dirty_metadata+0x1d1/0x590 fs/ext4/ext4_jbd2.c:364
 ext4_handle_dirty_dirblock+0x184/0x330 fs/ext4/namei.c:411
 add_dirent_to_buf+0x475/0x5e0 fs/ext4/namei.c:2042
 ext4_add_entry+0x665/0x2180 fs/ext4/namei.c:2252
 ext4_add_nondir+0x50/0x190 fs/ext4/namei.c:2586
 ext4_symlink+0x532/0x770 fs/ext4/namei.c:3415
 vfs_symlink+0x216/0x2d0 fs/namei.c:3960
 do_symlinkat+0xee/0x280 fs/namei.c:3987
 __do_sys_symlink fs/namei.c:4006 [inline]
 __se_sys_symlink fs/namei.c:4004 [inline]
 __x64_sys_symlink+0x32/0x40 fs/namei.c:4004
 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: 22000 Comm: syz-executor.1 Not tainted 5.10.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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