Re: [Xen-devel] dom0 / hypervisor hang on dom0 boot

[Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>]

Am Mittwoch 15 Mai 2013, 10:42:17 schrieb Jan Beulich:
> >>> On 15.05.13 at 11:12, Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx> wrote:
> > Am Mittwoch 15 Mai 2013, 09:35:46 schrieb Jan Beulich:
> >> >>> On 15.05.13 at 08:53, Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx> wrote:
> >> > I tried iommu=debug and I can't see any faulting messages but Iam not
> >> > familiar with this code.
> >> > I attached the logging, maybe anyone can have a look on this.
> 
> Perhaps only (if at all) by instrumenting the hypervisor. The
> question of course is how easily/quickly you can narrow down the
> code region that it might be dying in. And whether it's a hypervisor
> action at all that causes the hang (as opposed to something the
> DRM code in Dom0 does).

I added some debug code to the linux kernel and could track down the
point of the hang. I used openSuSE kernel 3.7.10-1.4 but I looked at newer
kernels and found that the code is similar.

i915_gem_init_global_gtt(...)
 ...
 intel_gtt_clear_range(start / PAGE_SIZE, (end-start) / PAGE_SIZE);
 ...

void intel_gtt_clear_range(unsigned int first_entry, unsigned int num_entries)
{
        unsigned int i;

    ---> A printk(...) here is seen on serial line!

        for (i = first_entry; i < (first_entry + num_entries); i++) {
                
intel_private.driver->write_entry(intel_private.base.scratch_page_dma,
                                                  i, 0);
        }

    ---> A printk(...) here is never seen!

        readl(intel_private.gtt+i-1);
}

The function behind the pointer intel_private.driver->write_entry is
i965_write_entry(). And the interesting instruction seems to be:
  writel(addr | pte_flags, intel_private.gtt + entry);

I added another printk() on start of the function i965_write_entry().
And surprisingly  after printing a lot of messages the kernel came up!!!
But now I had other problems like losing the audio device (maybe timeouts).
So maybe the hang is a timing problem?

What I wanted to check is, what the hypervisor is doing while the system hangs.
Has anybody an idea maybe a timer and after 30s printing a dump of the stack of
all cpus?
Thanks.

Dietmar.


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