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Re: [Qemu-devel] Regression on KVM qemu-system-aarch64 since "monitor: e

From: Auger Eric
Subject: Re: [Qemu-devel] Regression on KVM qemu-system-aarch64 since "monitor: enable IO thread for (qmp & !mux) typed"
Date: Wed, 28 Mar 2018 10:04:47 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

Hi Peter,

On 28/03/18 09:21, Peter Xu wrote:
> On Wed, Mar 28, 2018 at 08:49:59AM +0200, Auger Eric wrote:
>> Hi Peter,
>> On 28/03/18 04:03, Peter Xu wrote:
>>> On Fri, Mar 23, 2018 at 01:36:36PM +0100, Auger Eric wrote:
>>>> Hi,
>>>> On 23/03/18 13:11, Peter Maydell wrote:
>>>>> On 23 March 2018 at 12:01, Auger Eric <address@hidden> wrote:
>>>>>> Hi,
>>>>>> On 23/03/18 11:26, Peter Maydell wrote:
>>>>>>> On 23 March 2018 at 10:24, Auger Eric <address@hidden> wrote:
>>>>>>>> Hi,
>>>>>>>> I observe a regression on KVM accelerated qemu-system-aarch64:
>>>>>>>> Unexpected error in kvm_device_access() at
>>>>>>>> /home/augere/UPSTREAM/qemu/accel/kvm/kvm-all.c:2164:
>>>>>>>> 2018-03-23T09:59:59.629439Z qemu-system-aarch64: KVM_GET_DEVICE_ATTR
>>>>>>>> failed: Group 6 attr 0x000000000000c664: Device or resource busy
>>>>>>>> 2018-03-23 10:00:00.085+0000: shutting down, reason=crashed
>>>>>>> Can you get a backtrace for this? (I guess you'd need to fiddle
>>>>>>> with the kvm_device_access() code to make it assert rather
>>>>>>> than passing back the error).
>>>>>> OK. I will try to do so. As I could have expected, I cannot reproduce on
>>>>>> a standalone qemu command line. The problem observed above is seen with
>>>>>> libvirt launch which may be doing some other QMP stuff concurrently?
>>>>> Hmm, that could be a bit painful to debug. I dunno if libvirt
>>>>> has a "launch QEMU under gdb" option. If not, you could try
>>>>> something like:
>>>>>    if (condition we want to get a backtrace on) {
>>>>>        printf("hit condition, attach gdb to process %d\n", (int)getpid());
>>>>>        for (;;) { }
>>>>>    }
>>>> Thanks for the hint. Here is the stack I get.
>>>> #0  kvm_device_access (fd=31, group=6, attr=50788, val=0x5937c88, 
>>>> write=false, errp=0x16984a8 <error_abort>) at 
>>>> /home/augere/UPSTREAM/qemu/accel/kvm/kvm-all.c:2164
>>>> #1  0x00000000004f8ce4 in arm_gicv3_icc_reset (env=0xffffa1fc8330, 
>>>> ri=0x597f910) at /home/augere/UPSTREAM/qemu/hw/intc/arm_gicv3_kvm.c:632
>>>> #2  0x00000000006351ac in cp_reg_reset (key=0x597f730, value=0x597f910, 
>>>> opaque=0xffffa1fc0010) at /home/augere/UPSTREAM/qemu/target/arm/cpu.c:78
>>>> #3  0x0000ffffa47edce4 in g_hash_table_foreach () from 
>>>> /lib64/libglib-2.0.so.0
>>>> #4  0x0000000000635394 in arm_cpu_reset (s=0xffffa1fc0010) at 
>>>> /home/augere/UPSTREAM/qemu/target/arm/cpu.c:130
>>>> #5  0x000000000090c888 in cpu_reset (cpu=0xffffa1fc0010) at qom/cpu.c:249
>>>> #6  0x00000000005793d8 in do_cpu_reset (opaque=0xffffa1fc0010) at 
>>>> /home/augere/UPSTREAM/qemu/hw/arm/boot.c:665
>>>> #7  0x000000000073095c in qemu_devices_reset () at hw/core/reset.c:69
>>>> #8  0x00000000006976e0 in qemu_system_reset (reason=SHUTDOWN_CAUSE_NONE) 
>>>> at vl.c:1731
>>>> #9  0x000000000069fd60 in main (argc=69, argv=0xffffe877d1a8, 
>>>> envp=0xffffe877d3d8) at vl.c:4697
>>> I think current master should work fine with ARM KVM now since OOB is
>>> now off by default.
>> Yes it works for me with the reverts.
>>  But does ARM use postcopy, and will ARM need the
>>> coming network failure recovery feature?
>> I assume it does
>>> If so, maybe we'll still need to have a look on this single problem
>>> (this is the only non-testcase issue I know now with Out-Of-Band).
>> OK. I need to have a look at your series to better understand what it does.
> It introduced a dedicated iothread to run IO part of the monitor code
> (e.g., parsing of QMP input, and reply of the responses).  So now the
> parsing could start earlier, before the main loop (that's what I
> suspect the problem before), and meanwhile QMP IOs can happen in
> parallel now with main thread, which it never can before (since all
> QMP logic will be in main thread).
> I would be curious about what commands have been sent by libvirt to
> QEMU-arm when reach this point.  Please feel free to let me know if I
> can help in any form.  For example, if there is an ARM server that I
> can login and run both libvirt and QEMU, I'd be glad to play with it
> too.
Yes, I will send you the data and will my utmost to help in the debugging.


> Thanks,

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