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

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
>>>>   Loader:        0000000000100000->000000000019bd04
>>>>   TOTAL:         0000000000000000->00000000ff800000
>>>>   ENTRY ADDRESS: 0000000000100000
>>>>   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 think, in 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?

I'm looking into it. I suspicion is that

  if (msg.type != type)

in xs_talkv() is true.


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