Re: [Xen-devel] libxl: cannot start guest

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On 05/22/12 15:18, Christoph Egger wrote:

> On 05/22/12 14:53, Ian Campbell wrote:
> 
>> On Tue, 2012-05-22 at 13:35 +0100, Christoph Egger wrote:
>>> On 05/21/12 17:57, Ian Campbell wrote:
>>>
>>>>> libxl: debug: libxl_device.c:183:libxl__device_disk_set_backend: Disk
>>>>> vdev=hda spec.backend=unknown
>>>>> libxl: debug: libxl_device.c:219:libxl__device_disk_set_backend: Disk
>>>>> vdev=hda, using backend phy
>>>>> xc: detail: elf_parse_binary: phdr: paddr=0x100000 memsz=0x9bd04
>>>>> xc: detail: elf_parse_binary: memory: 0x100000 -> 0x19bd04
>>>>> xc: info: VIRTUAL MEMORY ARRANGEMENT:
>>>>>   Loader:        0000000000100000->000000000019bd04
>>>>>   TOTAL:         0000000000000000->00000000ff800000
>>>>>   ENTRY ADDRESS: 0000000000100000
>>>>> xc: info: PHYSICAL MEMORY ALLOCATION:
>>>>>   4KB PAGES: 0x0000000000000200
>>>>>   2MB PAGES: 0x00000000000003fb
>>>>>   1GB PAGES: 0x0000000000000002
>>>>> xc: detail: elf_load_binary: phdr 0 at 0x0x7f7ff7f42000 -> 
>>>>> 0x0x7f7ff7fd4b74
>>>>> libxl: error: libxl.c:3213:libxl_sched_credit_domain_set: Cpu weight out
>>>>> of range, valid values are within range from 1 to 65535
>>>>> libxl: error: libxl_dom.c:74:libxl__sched_set_params:
>>>>> libxl_sched_credit_domain_set failed -6
>>>>> libxl: debug: libxl_device.c:183:libxl__device_disk_set_backend: Disk
>>>>> vdev=hda spec.backend=phy
>>>>> libxl: error: libxl_xshelp.c:102:libxl__xs_get_dompath: failed to get
>>>>> dompath for 7: Bad file descriptor
>>>>
>>>> This is back to the original issue, I think the last couple of mails
>>>> have been something of a tangent since you weren't getting as far as
>>>> this failure.
>>>>
>>>> I'm not really sure what to suggest here -- something is either closing
>>>> the fd or scribbling over the memory which contains it.
>>>>
>>>> I suppose you could sprinkle calls to libxl__xs_get_dompath() around
>>>> between libxl__sched_set_params and libxl__device_disk_set_backend and
>>>> see where it starts failing -- that's going to be pretty tedious though.
>>>
>>>
>>> It starts failing in libxl__build_post() right after
>>> xs_introduce_domain().
>>
>> What method did you use to determine that?
> 
> 
> 
> 
> What you said:
> 
> "sprinkle calls to libxl__xs_get_dompath() around between
> libxl__sched_set_params and libxl__device_disk_set_backend and
> see where it starts failing"
> 
>  > So at the xs_transaction_end right before that ctx->xsh is valid, but
> 
>> right after...
>>         xs_introduce_domain(ctx->xsh, domid, state->store_mfn, 
>> state->store_port);
>> ...it is invalid? i.e. before the free(vmpath) it is already corrupt?
> 
> 
> 
> 
> Yes, you got it.
> 
>>
>> (Aside: why isn't vmpath in the gc, instead of done manually,
>> nevermind...)
>>
>> Does the xs_introduce_domain itself succeed?
> 
> 
> 
> 
> No, it fails.
> 
>> Or do you mean that the next use of xsh after this fails
> 
>> (where is that, somewhere back up the callchain? store_libxl_entry
>> perhaps?)
> 
>>
>> xs_introduce_domain doesn't seem to do much which is untoward with the
>> handle.
> 
> 
> 
> I thinkIn xs_talkv() something must fail.
> 
>> The only thing which springs to mind is that it may generate an
>> @IntroduceDomain watch event. However xl is single threaded so we won't
>> process that event until we unwind to whichever point we do an event
>> loop iteration, in which case the corruption would have to happen later
>> than right after xs_introduce_domain().
>>
>> Did you manage to determine if "Bad file descriptor" was due to it being
>> closed vs. the value being corrupted?
> 
> My suspicion is that
> 
>    if (msg.type != type)
> 
> in xs_talkv() is true.
> 
> Christoph


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