Date:   Thu, 16 Jul 2020 09:26:12 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Salil Mehta <salil.mehta@...wei.com>
Cc:     yuzenghui <yuzenghui@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        "Zhuangyuzeng (Yisen)" <yisen.zhuang@...wei.com>,
        "Wanghaibin (D)" <wanghaibin.wang@...wei.com>
Subject: Re: [REPORT] possible circular locking dependency when booting a VM
 on arm64 host

On 2020-07-16 01:58, Salil Mehta wrote:
>> From: Marc Zyngier [mailto:maz@...nel.org]
>> Sent: Wednesday, July 15, 2020 5:09 PM
>> To: yuzenghui <yuzenghui@...wei.com>
>> 
>> Hi Zenghui,
>> 
>> On 2020-07-09 11:41, Zenghui Yu wrote:
>> > Hi All,
>> >
>> > I had seen the following lockdep splat when booting a guest on my
>> > Kunpeng 920 with GICv4 enabled. I can also trigger the same splat
>> > on v5.5 so it should already exist in the kernel for a while. I'm
>> > not sure what the exact problem is and hope someone can have a look!
>> 
>> I can't manage to trigger this splat on my D05, despite running guests
>> with GICv4 enabled. A couple of questions below:
> 
> 
> Sorry I forgot to update but I did try on Friday and I could not manage
> to trigger it on D06/Kunpeng920 either. I used 5.8.0-rc4.
> 
> 
>> > Thanks,
>> > Zenghui
>> >
>> > [  103.855511] ======================================================
>> > [  103.861664] WARNING: possible circular locking dependency detected
>> > [  103.867817] 5.8.0-rc4+ #35 Tainted: G        W
>> > [  103.872932] ------------------------------------------------------
>> > [  103.879083] CPU 2/KVM/20515 is trying to acquire lock:
>> > [  103.884200] ffff202fcd5865b0 (&irq_desc_lock_class){-.-.}-{2:2},
>> > at: __irq_get_desc_lock+0x60/0xa0
>> > [  103.893127]
>> >                but task is already holding lock:
>> > [  103.898933] ffff202fcfd07f58 (&rq->lock){-.-.}-{2:2}, at:
>> > __schedule+0x114/0x8b8
>> > [  103.906301]
>> >                which lock already depends on the new lock.
>> >
>> > [  103.914441]
>> >                the existing dependency chain (in reverse order) is:
>> > [  103.921888]
>> >                -> #3 (&rq->lock){-.-.}-{2:2}:
>> > [  103.927438]        _raw_spin_lock+0x54/0x70
>> > [  103.931605]        task_fork_fair+0x48/0x150
>> > [  103.935860]        sched_fork+0x100/0x268
>> > [  103.939856]        copy_process+0x628/0x1868
>> > [  103.944106]        _do_fork+0x74/0x710
>> > [  103.947840]        kernel_thread+0x78/0xa0
>> > [  103.951917]        rest_init+0x30/0x270
>> > [  103.955742]        arch_call_rest_init+0x14/0x1c
>> > [  103.960339]        start_kernel+0x534/0x568
>> > [  103.964503]
>> >                -> #2 (&p->pi_lock){-.-.}-{2:2}:
>> > [  103.970224]        _raw_spin_lock_irqsave+0x70/0x98
>> > [  103.975080]        try_to_wake_up+0x5c/0x5b0
>> > [  103.979330]        wake_up_process+0x28/0x38
>> > [  103.983581]        create_worker+0x128/0x1b8
>> > [  103.987834]        workqueue_init+0x308/0x3bc
>> > [  103.992172]        kernel_init_freeable+0x180/0x33c
>> > [  103.997027]        kernel_init+0x18/0x118
>> > [  104.001020]        ret_from_fork+0x10/0x18
>> > [  104.005097]
>> >                -> #1 (&pool->lock){-.-.}-{2:2}:
>> > [  104.010817]        _raw_spin_lock+0x54/0x70
>> > [  104.014983]        __queue_work+0x120/0x6e8
>> > [  104.019146]        queue_work_on+0xa0/0xd8
>> > [  104.023225]        irq_set_affinity_locked+0xa8/0x178
>> > [  104.028253]        __irq_set_affinity+0x5c/0x90
>> > [  104.032762]        irq_set_affinity_hint+0x74/0xb0
>> > [  104.037540]        hns3_nic_init_irq+0xe0/0x210 [hns3]
>> > [  104.042655]        hns3_client_init+0x2d8/0x4e0 [hns3]
>> > [  104.047779]        hclge_init_client_instance+0xf0/0x3a8 [hclge]
>> > [  104.053760]        hnae3_init_client_instance.part.3+0x30/0x68
>> > [hnae3]
>> > [  104.060257]        hnae3_register_ae_dev+0x100/0x1f0 [hnae3]
>> > [  104.065892]        hns3_probe+0x60/0xa8 [hns3]
>> 
>> Are you performing some kind of PCIe hot-plug here? Or is that done
>> at boot only? It seems to help triggering the splat.
> 
> 
> I am not sure how you can do that since HNS3 is integrated NIC so
> physical hot-plug is definitely ruled out. local_pci_probe()
> should also get called when we insert the hns3_enet module which
> eventually initializes the driver.
> 
> 
>> > [  104.070319]        local_pci_probe+0x44/0x98
>> > [  104.074573]        work_for_cpu_fn+0x20/0x30
>> > [  104.078823]        process_one_work+0x258/0x618
>> > [  104.083333]        worker_thread+0x1c0/0x438
>> > [  104.087585]        kthread+0x120/0x128
>> > [  104.091318]        ret_from_fork+0x10/0x18
>> > [  104.095394]
>> >                -> #0 (&irq_desc_lock_class){-.-.}-{2:2}:
>> > [  104.101895]        __lock_acquire+0x11bc/0x1530
>> > [  104.106406]        lock_acquire+0x100/0x3f8
>> > [  104.110570]        _raw_spin_lock_irqsave+0x70/0x98
>> > [  104.115426]        __irq_get_desc_lock+0x60/0xa0
>> > [  104.120021]        irq_set_vcpu_affinity+0x48/0xc8
>> > [  104.124793]        its_make_vpe_non_resident+0x6c/0xc0
>> > [  104.129910]        vgic_v4_put+0x64/0x70
>> > [  104.133815]        vgic_v3_put+0x28/0x100
>> > [  104.137806]        kvm_vgic_put+0x3c/0x60
>> > [  104.141801]        kvm_arch_vcpu_put+0x38/0x58
>> > [  104.146228]        kvm_sched_out+0x38/0x58
>> > [  104.150306]        __schedule+0x554/0x8b8
>> > [  104.154298]        schedule+0x50/0xe0
>> > [  104.157946]        kvm_arch_vcpu_ioctl_run+0x644/0x9e8
>> > [  104.163063]        kvm_vcpu_ioctl+0x4b4/0x918
>> > [  104.167403]        ksys_ioctl+0xb4/0xd0
>> > [  104.171222]        __arm64_sys_ioctl+0x28/0xc8
>> > [  104.175647]        el0_svc_common.constprop.2+0x74/0x138
>> > [  104.180935]        do_el0_svc+0x34/0xa0
>> > [  104.184755]        el0_sync_handler+0xec/0x128
>> > [  104.189179]        el0_sync+0x140/0x180
>> > [  104.192997]
>> 
>> The kernel seems to scream at us because we have two paths
>> exercising  the irq_desc_lock_class, one holding the rq->lock
>> because we are on the schedule out path.
>> 
>> These two locks are somehow unrelated (they just belong to the
>> same class), but the kernel cannot know that.
> 
> 
> Sure. I understand that part. But if this is a ABBA type deadlock
> then beside the irq_desc lock the rq->lock should belong to the
> same runqueue which effectively means the 2 context of the hns and
> the VM are referring to same cpu?

They may have happened on the same CPU *at some point*. Not necessarily
at the point of the splat (this is a lock class, not a single lock).

>> Not quite sure how to solve it though. The set_vcpu_affinity
>> call is necessary on the preemption path in order to make the
>> vpe non-resident. But it would help if I could reproduce it...
> 
> 
> Sure. That also means if the lock ordering has to be imposed then
> perhaps it has to be taken care from the other context of hns3.
> 
> One way is to avoid calling irq_set_affinity_hint() during 
> initialization
> but this does not guarantees that this conflict will not happen in 
> future
> while using irq_set_affinity_hint() as it is well possible that VM is 
> again
> about to be scheduled out at that time.

No, the issue is with the affinity notifier, not with the affinity
setting itself. It is the one that implies irq_desc_lock -> rq->lock.

> 
> Also, I think this problem should appear even if we use Intel NIC and
> perform the same set of steps.

I'm using an Intel X540 without any issue, but that's irrelevant.

This is a general problem of using anything having any impact on
an interrupt) from the schedule() path, which triggers either
rq->lock -> irq_desc_lock OR the opposite one, depending where
you are coming from.

Both behavior exist in the kernel today, and it is hard to picture
why one would be more valid than the other.

         M.
-- 
Jazz is not dead. It just smells funny...

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