syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-....: (1 GPs behind) idle=402/1/0x4000000000000000 softirq=103426/103427 fqs=5233 
	(t=10501 jiffies g=188617 q=1397)
NMI backtrace for cpu 1
CPU: 1 PID: 5204 Comm: syz-executor.3 Not tainted 5.13.0-rc2-next-20210518-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x13e/0x1d6 lib/dump_stack.c:129
 nmi_cpu_backtrace.cold+0x44/0xd7 lib/nmi_backtrace.c:105
 nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x25e/0x3f0 kernel/rcu/tree_stall.h:342
 print_cpu_stall kernel/rcu/tree_stall.h:625 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:700 [inline]
 rcu_pending kernel/rcu/tree.c:3922 [inline]
 rcu_sched_clock_irq.cold+0x3f1/0x74b kernel/rcu/tree.c:2641
 update_process_times+0x16d/0x200 kernel/time/timer.c:1782
 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:226
 tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1420
 __run_hrtimer kernel/time/hrtimer.c:1537 [inline]
 __hrtimer_run_queues+0x1c0/0xe50 kernel/time/hrtimer.c:1601
 hrtimer_interrupt+0x330/0xa00 kernel/time/hrtimer.c:1663
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1089 [inline]
 __sysvec_apic_timer_interrupt+0x146/0x530 arch/x86/kernel/apic/apic.c:1106
 sysvec_apic_timer_interrupt+0x8e/0xc0 arch/x86/kernel/apic/apic.c:1100
 </IRQ>
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:647
RIP: 0010:slow_down_io arch/x86/include/asm/paravirt.h:55 [inline]
RIP: 0010:inb_p arch/x86/include/asm/io.h:334 [inline]
RIP: 0010:vga_io_r include/video/vga.h:204 [inline]
RIP: 0010:vga_io_rgfx include/video/vga.h:389 [inline]
RIP: 0010:setcolor drivers/video/fbdev/vga16fb.c:170 [inline]
RIP: 0010:vga_imageblit_expand drivers/video/fbdev/vga16fb.c:1164 [inline]
RIP: 0010:vga16fb_imageblit+0x929/0x2200 drivers/video/fbdev/vga16fb.c:1260
Code: c7 c2 a0 01 ff 8b 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 b2 15 00 00 ff 15 5d cd f5 07 ba cf 03 00 00 ec <48> c7 c2 a0 01 ff 8b 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80
RSP: 0018:ffffc90002986e50 EFLAGS: 00000246
RAX: dffffc00000000ff RBX: 0000000000000000 RCX: ffffc90015dea000
RDX: 00000000000003cf RSI: ffffffff84093270 RDI: ffffc90002986fe8
RBP: ffffc90002986fdc R08: 0000000000000000 R09: 0000000000000001
R10: ffffffff84093263 R11: 0000000000000001 R12: ffffffff81329c30
R13: ffff88801b714eee R14: ffffc90002986ff8 R15: ffffc90002986fd8
 bit_putcs_unaligned drivers/video/fbdev/core/bitblit.c:139 [inline]
 bit_putcs+0x6e1/0xd20 drivers/video/fbdev/core/bitblit.c:188
 fbcon_putcs+0x35a/0x450 drivers/video/fbdev/core/fbcon.c:1296
 fbcon_redraw.constprop.0+0x41a/0x4b0 drivers/video/fbdev/core/fbcon.c:1672
 fbcon_scroll+0x1d7a/0x3580 drivers/video/fbdev/core/fbcon.c:1782
 con_scroll+0x5b9/0x6d0 drivers/tty/vt/vt.c:630
 lf+0x26b/0x2c0 drivers/tty/vt/vt.c:1490
 vc_con_write_normal drivers/tty/vt/vt.c:2811 [inline]
 do_con_write+0xf1c/0x1e40 drivers/tty/vt/vt.c:2915
 con_put_char+0x70/0xa0 drivers/tty/vt/vt.c:3263
 tty_put_char+0xb7/0x150 drivers/tty/tty_io.c:3180
 do_output_char+0x155/0x850 drivers/tty/n_tty.c:485
 process_output drivers/tty/n_tty.c:511 [inline]
 n_tty_write+0x4c3/0xfd0 drivers/tty/n_tty.c:2300
 do_tty_write drivers/tty/tty_io.c:1042 [inline]
 file_tty_write.constprop.0+0x526/0x910 drivers/tty/tty_io.c:1131
 call_write_iter include/linux/fs.h:2114 [inline]
 do_iter_readv_writev+0x46f/0x740 fs/read_write.c:740
 do_iter_write+0x188/0x670 fs/read_write.c:866
 vfs_iter_write+0x70/0xa0 fs/read_write.c:907
 iter_file_splice_write+0x723/0xc70 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x110/0x180 fs/splice.c:936
 splice_direct_to_actor+0x34b/0x8c0 fs/splice.c:891
 do_splice_direct+0x1b3/0x280 fs/splice.c:979
 do_sendfile+0x9f0/0x1120 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1311
 do_syscall_64+0x31/0xb0 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4665d9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd84f3c9188 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 000000000056c0f0 RCX: 00000000004665d9
RDX: 0000000000000000 RSI: 0000000000000008 RDI: 0000000000000007
RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000
R10: 0800000080004103 R11: 0000000000000246 R12: 000000000056c0f0
R13: 00007ffe40adce2f R14: 00007fd84f3c9300 R15: 0000000000022000