Re: [Xen-devel] Hypercall continuation and wait_event

[Keir Fraser <keir.xen@xxxxxxxxx>]

Not sure. Did you snip some lines from the call trace that might explain why
the call trace is being generated (e.g., watchdog timeout, page fault, ...)?
>From the lines you provide, we can't even tell which vcpu it is that is
dumping the call trace.

 -- Keir

On 09/04/2012 22:19, "Ruslan Nikolaev" <nruslan_devel@xxxxxxxxx> wrote:

> Keir,
> 
> Thanks again! When I used the scheme I have described, I periodically receive
> kernel errors as shown below. Notice that I use HVM domain and also 'isolcpus'
> as a Linux kernel option to prevent a dedicated VCPU from being normally used.
> A hypercall is being made from a special kernel thread (which is bind to the
> dedicated VCPU before the call).
> 
> What could be the reason of these messages? Looks like it is something related
> to a timer.
> 
> 
> [ 1039.319957] RIP: 0010:[<ffffffff8101ba09>]  [<ffffffff8101ba09>]
> default_send_IPI_mask_sequence_phys+0x95/0xce
> [ 1039.319957] RSP: 0018:ffff88007f043c28  EFLAGS: 00000046
> [ 1039.319957] RAX: 0000000000000400 RBX: 0000000000000096 RCX:
> 0000000000000020
> [ 1039.319957] RDX: 0000000000000002 RSI: 0000000000000020 RDI:
> 0000000000000300
> [ 1039.319957] RBP: ffff88007f043c68 R08: 0000000000000000 R09:
> ffffffff8163eb20
> [ 1039.319957] R10: ffff8800ff043bad R11: 0000000000000000 R12:
> 000000000000d602
> [ 1039.319957] R13: 0000000000000002 R14: 0000000000000400 R15:
> ffffffff8163eb20
> [ 1039.319957] FS:  0000000000000000(0000) GS:ffff88007f040000(0000)
> knlGS:0000000000000000
> [ 1039.319957] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [ 1039.319957] CR2: 00007f74195d29be CR3: 000000007af4d000 CR4:
> 00000000000006a0
> [ 1039.319957] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [ 1039.319957] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
> 0000000000000400
> [ 1039.319957] Process swapper/2 (pid: 0, threadinfo ffff88007c4ec000, task
> ffff88007c4f1650)
> [ 1039.319957] Stack:
> [ 1039.319957]  0000000000000002 0000000400000008 ffff88007f043c88
> 0000000000002710
> [ 1039.319957]  ffffffff8161a280 ffffffff8161a340 0000000000000001
> ffffffff8161a4c0
> [ 1039.319957]  ffff88007f043c78 ffffffff8101ecc6 ffff88007f043c98
> ffffffff8101bb81
> [ 1039.319957] Call Trace:
> [ 1039.319957]  <IRQ>
> [ 1039.319957]  [<ffffffff8101ecc6>] physflat_send_IPI_all+0x12/0x14
> [ 1039.319957]  [<ffffffff8101bb81>] arch_trigger_all_cpu_backtrace+0x4b/0x6e
> [ 1039.319957]  [<ffffffff8107a25a>] __rcu_pending+0x224/0x347
> [ 1039.319957]  [<ffffffff8107aa13>] rcu_check_callbacks+0xa2/0xb4
> [ 1039.319957]  [<ffffffff810469fd>] update_process_times+0x3a/0x70
> [ 1039.319957]  [<ffffffff8105f815>] tick_sched_timer+0x70/0x9a
> [ 1039.319957]  [<ffffffff810557c0>] __run_hrtimer.isra.26+0x75/0xce
> [ 1039.319957]  [<ffffffff81055ded>] hrtimer_interrupt+0xd7/0x193
> [ 1039.319957]  [<ffffffff81005f0a>] xen_timer_interrupt+0x2f/0x155
> [ 1039.319957]  [<ffffffff81021945>] ? pvclock_clocksource_read+0x48/0xb4
> [ 1039.319957]  [<ffffffff81021945>] ? pvclock_clocksource_read+0x48/0xb4
> [ 1039.319957]  [<ffffffff81021945>] ? pvclock_clocksource_read+0x48/0xb4
> [ 1039.319957]  [<ffffffff8107542d>] handle_irq_event_percpu+0x29/0x126
> [ 1039.319957]  [<ffffffff8119064a>] ? info_for_irq+0x9/0x19
> [ 1039.319957]  [<ffffffff81077b70>] handle_percpu_irq+0x39/0x4d
> [ 1039.319957]  [<ffffffff81190510>] __xen_evtchn_do_upcall+0x147/0x1df
> [ 1039.319957]  [<ffffffff81191eae>] xen_evtchn_do_upcall+0x27/0x39
> [ 1039.319957]  [<ffffffff812987ee>] xen_hvm_callback_vector+0x6e/0x80
> [ 1039.319957]  <EOI>
> [ 1039.319957]  [<ffffffff8107ab83>] ? rcu_needs_cpu+0x110/0x1c1
> [ 1039.319957]  [<ffffffff81020ff0>] ? native_safe_halt+0x6/0x8
> [ 1039.319957]  [<ffffffff8100e8bf>] default_idle+0x27/0x44
> [ 1039.319957]  [<ffffffff81007704>] cpu_idle+0x66/0xa4
> [ 1039.319957]  [<ffffffff81286605>] start_secondary+0x1ac/0x1b1
> 
> 
> 
> Thanks,
> Ruslan
> 
> 
> ----- Original Message -----
> From: Keir Fraser <keir.xen@xxxxxxxxx>
> To: Ruslan Nikolaev <nruslan_devel@xxxxxxxxx>; "xen-devel@xxxxxxxxxxxxx"
> <xen-devel@xxxxxxxxxxxxx>
> Cc: 
> Sent: Monday, April 9, 2012 8:58 PM
> Subject: Re: [Xen-devel] Hypercall continuation and wait_event
> 
> It means the vcpu has an interrupt pending (in the pv case, that means an
> event channel has a pending event).
> 
> 
> On 09/04/2012 21:16, "Ruslan Nikolaev" <nruslan_devel@xxxxxxxxx> wrote:
> 
>> Keir,
>> 
>> Thanks for your replies! Just one more question about
>> local_event_need_delivery(). Under what (common) conditions I would expect to
>> have local events that need delivery?
>> 
>> Ruslan
>> 
>> 
>> 
>> ----- Original Message -----
>> From: Keir Fraser <keir.xen@xxxxxxxxx>
>> To: Ruslan Nikolaev <nruslan_devel@xxxxxxxxx>; "xen-devel@xxxxxxxxxxxxx"
>> <xen-devel@xxxxxxxxxxxxx>
>> Cc: 
>> Sent: Monday, April 9, 2012 8:09 PM
>> Subject: Re: [Xen-devel] Hypercall continuation and wait_event
>> 
>> On 09/04/2012 20:18, "Ruslan Nikolaev" <nruslan_devel@xxxxxxxxx> wrote:
>> 
>>> Thanks for the reply.
>>> 
>>> Since it can take arbitrarily long for an event to arrive (e.g., it is
>>> coming
>>> from a different guest on a user request), how do I need to handle this
>>> case?Does it mean that I only need to make sure that nothings get scheduled
>>> on
>>> this VCPU in the guest?
>> 
>> Nothing else *can* get scheduled on this VCPU in the guest. The VCPU will
>> sleep within wait_event within the hypercall context. Hence you must not
>> hold any hypervisor spinlocks either, for example.
>> 
>>> Also, it is not exactly clear to me how wait_event avoids the need for
>>> hypercall continuation. What about local_events_need_delivery() or
>>> softirq_pending()? Are they going to be handled by wait_event internally?
>> 
>> Your VCPU gets descheduled. Hence softirq_pending() is not your concern for
>> the duration that you're descheduled. And if local_event_need_delivery(),
>> that's too bad, they have to wait for the vcpu to wake up on the event.
>> 
>> -- Keir
>> 
>>> Ruslan
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> ----- Original Message -----
>>> From: Keir Fraser <keir.xen@xxxxxxxxx>
>>> To: Ruslan Nikolaev <nruslan_devel@xxxxxxxxx>; "xen-devel@xxxxxxxxxxxxx"
>>> <xen-devel@xxxxxxxxxxxxx>
>>> Cc: 
>>> Sent: Monday, April 9, 2012 6:54 PM
>>> Subject: Re: [Xen-devel] Hypercall continuation and wait_event
>>> 
>>> On 09/04/2012 18:51, "Ruslan Nikolaev" <nruslan_devel@xxxxxxxxx> wrote:
>>> 
>>>> Hi
>>>> 
>>>> I am curious how I can properly support hypercall continuation and
>>>> wait_event.
>>>> I have a dedicated VCPU in a domain which makes a special hypercall, and
>>>> the
>>>> hypercall waits for certain event to arrive. I am using queues available in
>>>> Xen, so wait_event will be invoked in the hypercall once its ready to
>>>> accept
>>>> events. However, my understanding that even though I have a dedicated VCPU
>>>> for
>>>> this hypercall, I still may need to support hypercall continuation
>>>> properly.
>>>> (Is this the case?) So, my question is how exactly the need for hypercall
>>> 
>>> No it's not the case, the old hypercall_create_continuation() mechanism does
>>> not need to be used with wait_event().
>>> 
>>> -- Keir
>>> 
>>>> preemption may affect wait_event() and wait() operations, and where would I
>>>> need to do hypercall_preempt_check()?
>>>> 
>>>> Thank you!
>>>> Ruslan
>>>> 
>>>> 
>>>> _______________________________________________
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>>>> Xen-devel@xxxxxxxxxxxxx
>>>> http://lists.xen.org/xen-devel
>>> 
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>> 
>> 
>> 
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