Re: WARNING: suspicious RCU usage - while installing a VM on a CPU listed under nohz_full

[Nitesh Narayan Lal <nitesh@redhat.com>]

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On 7/29/20 8:34 AM, Nitesh Narayan Lal wrote:
> On 7/28/20 10:38 PM, Wanpeng Li wrote:
>> Hi Nitesh，
>> On Wed, 29 Jul 2020 at 09:00, Wanpeng Li <kernellwp@gmail.com> wrote:
>>> On Tue, 28 Jul 2020 at 22:40, Nitesh Narayan Lal <nitesh@redhat.com> wrote:
>>>> Hi,
>>>>
>>>> I have recently come across an RCU trace with the 5.8-rc7 kernel that has the
>>>> debug configs enabled while installing a VM on a CPU that is listed under
>>>> nohz_full.
>>>>
>>>> Based on some of the initial debugging, my impression is that the issue is
>>>> triggered because of the fastpath that is meant to optimize the writes to x2APIC
>>>> ICR that eventually leads to a virtual IPI in fixed delivery mode, is getting
>>>> invoked from the quiescent state.
>> Could you try latest linux-next tree? I guess maybe some patches are
>> pending in linux-next tree, I can't reproduce against linux-next tree.
> Sure, I will try this today.

Hi Wanpeng,

I am not seeing the issue getting reproduced with the linux-next tree.
Although, I am still seeing a Warning stack trace:

[  139.220080] RIP: 0010:kvm_arch_vcpu_ioctl_run+0xb57/0x1320 [kvm]
[  139.226837] Code: e8 03 0f b6 04 18 84 c0 74 06 0f 8e 4a 03 00 00 41 c6 85 48
31 00 00 00 e9 24 f8 ff ff 4c 89 ef e8 7e ac 02 00 e9 3d f8 ff ff <0f> 0b e9 f2
f8 ff ff 48f
[  139.247828] RSP: 0018:ffff8889bc397cb8 EFLAGS: 00010202
[  139.253700] RAX: 0000000000000001 RBX: dffffc0000000000 RCX: ffffffffc1fc3bef
[  139.261695] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff888f0fa1a8a0
[  139.269692] RBP: ffff8889bc397d18 R08: ffffed113786a7d0 R09: ffffed113786a7d0
[  139.277686] R10: ffff8889bc353e7f R11: ffffed113786a7cf R12: ffff8889bc35423c
[  139.285682] R13: ffff8889bc353e40 R14: ffff8889bc353e6c R15: ffff88897f536000
[  139.293678] FS:  00007f3d8a71c700(0000) GS:ffff888a3c400000(0000)
knlGS:0000000000000000
[  139.302742] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  139.309186] CR2: 0000000000000000 CR3: 00000009bc34c004 CR4: 00000000003726e0
[  139.317180] Call Trace:
[  139.320002]  kvm_vcpu_ioctl+0x3ee/0xb10 [kvm]
[  139.324907]  ? sched_clock+0x5/0x10
[  139.328875]  ? kvm_io_bus_get_dev+0x1c0/0x1c0 [kvm]
[  139.334375]  ? ioctl_file_clone+0x120/0x120
[  139.339079]  ? selinux_file_ioctl+0x98/0x570
[  139.343895]  ? selinux_file_mprotect+0x5b0/0x5b0
[  139.349088]  ? irq_matrix_assign+0x360/0x430
[  139.353904]  ? rcu_read_lock_sched_held+0xe0/0xe0
[  139.359201]  ? __fget_files+0x1f0/0x300
[  139.363532]  __x64_sys_ioctl+0x128/0x18e
[  139.367948]  do_syscall_64+0x33/0x40
[  139.371974]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  139.377643] RIP: 0033:0x7f3d98d0a88b

Are you also triggering anything like this in your environment?


>
-- 
Nitesh


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