INFO: rcu detected stall in x86_decode_insn

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 3d0e7a9e00fd Merge tag 'md/4.19-rc2' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13c50dea400000
kernel config: https://syzkaller.appspot.com/x/.config?x=8f59875069d721b6
dashboard link: https://syzkaller.appspot.com/bug?extid=2c77fce0ff7df8d74b3a
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [h...@zytor.com k...@vger.kernel.org
linux-...@vger.kernel.org mi...@redhat.com pbon...@redhat.com
rkr...@redhat.com tg...@linutronix.de x...@kernel.org]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2c77fc...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: (detected by 0, t=10502 jiffies, g=11449, q=370)
rcu: All QSes seen, last rcu_preempt kthread activity 10501
(4294970610-4294960109), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor2 R running task 21632 8354 5485 0x00000000
Call Trace:
<IRQ>
sched_show_task.cold.83+0x2b6/0x30a kernel/sched/core.c:5296
print_other_cpu_stall.cold.79+0xa83/0xba5 kernel/rcu/tree.c:1430
check_cpu_stall kernel/rcu/tree.c:1557 [inline]
__rcu_pending kernel/rcu/tree.c:3276 [inline]
rcu_pending kernel/rcu/tree.c:3319 [inline]
rcu_check_callbacks+0xafc/0x1990 kernel/rcu/tree.c:2665
update_process_times+0x2d/0x70 kernel/time/timer.c:1636
tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164
tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
__run_hrtimer kernel/time/hrtimer.c:1398 [inline]
__hrtimer_run_queues+0x41c/0x10d0 kernel/time/hrtimer.c:1460
hrtimer_interrupt+0x313/0x780 kernel/time/hrtimer.c:1518
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1029 [inline]
smp_apic_timer_interrupt+0x1a1/0x760 arch/x86/kernel/apic/apic.c:1054
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:864
</IRQ>
RIP: 0010:desc_limit_scaled arch/x86/kvm/emulate.c:581 [inline]
RIP: 0010:__linearize arch/x86/kvm/emulate.c:724 [inline]
RIP: 0010:__do_insn_fetch_bytes+0x2d9/0x950 arch/x86/kvm/emulate.c:879
Code: 48 b8 00 00 00 00 00 fc ff df 0f b6 04 02 48 89 fa 83 e2 07 38 d0 7f
08 84 c0 0f 85 cb 05 00 00 31 ff 44 89 fe e8 57 47 6a 00 <45> 84 ff 0f 88
68 03 00 00 e8 79 46 6a 00 41 0f b6 46 c5 bf 04 00
RSP: 0018:ffff88018d2ceae8 EFLAGS: 00000297 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000002 RBX: ffff88018d6b3ce0 RCX: ffffffff811488b9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
RBP: ffff88018d2cebe8 R08: ffff88018d6ba380 R09: ffff88018d6b3e00
R10: ffffed0031ad67c1 R11: ffff88018d6b3e0b R12: 0000000000000000
R13: ffff88018d2ceb80 R14: ffff88018d2cebc0 R15: 0000000000000000
x86_decode_insn+0x1544/0x54c0 arch/x86/kvm/emulate.c:5107
x86_emulate_instruction+0x89a/0x1f90 arch/x86/kvm/x86.c:6175
kvm_mmu_page_fault+0x342/0x1ad0 arch/x86/kvm/mmu.c:5276
handle_ept_violation+0x29e/0x6a0 arch/x86/kvm/vmx.c:7679
vmx_handle_exit+0x2f7/0x17f0 arch/x86/kvm/vmx.c:10115
vcpu_enter_guest+0x14a9/0x62e0 arch/x86/kvm/x86.c:7630
vcpu_run arch/x86/kvm/x86.c:7693 [inline]
kvm_arch_vcpu_ioctl_run+0x375/0x16e0 arch/x86/kvm/x86.c:7870
kvm_vcpu_ioctl+0x72b/0x1150 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2590
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:501 [inline]
do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702
__do_sys_ioctl fs/ioctl.c:709 [inline]
__se_sys_ioctl fs/ioctl.c:707 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457099
Code: fd b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f02fd19dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f02fd19e6d4 RCX: 0000000000457099
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000006
RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004cf730 R14: 00000000004c59b9 R15: 0000000000000000
rcu: rcu_preempt kthread starved for 10602 jiffies! g11449 f0x2
RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt R running task 22360 10 2 0x80000000
Call Trace:
context_switch kernel/sched/core.c:2825 [inline]
__schedule+0x86c/0x1ed0 kernel/sched/core.c:3473
schedule+0xfe/0x460 kernel/sched/core.c:3517
schedule_timeout+0x140/0x260 kernel/time/timer.c:1804
rcu_gp_kthread+0x9d9/0x2310 kernel/rcu/tree.c:2194
kthread+0x35a/0x420 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:413


---
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[Dmitry Vyukov]

#syz dup: INFO: rcu detected stall in kvm_vcpu_ioctl

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