Re: Fwd: Debugging "Xen BUG at ... list.h" on ARM

[Julien Grall <julien.grall@linaro.org>]

(Adding a couple of people in cc)

On 14/04/14 09:02, Thomas Leonard wrote:
> Hi all,

Hello,

> I'm new to Xen, and trying to get the arm32 port of Mini-OS working on
> a Cubieboard2. I have the board running an Ubuntu Dom0 and an Ubuntu
> guest happily, and I've written up the instructions for that here:
>
>    https://github.com/talex5/mirage-www/blob/master/tmpl/wiki/xen-on-cubieboard2.md
>
> However, while trying to get a Mini-OS domU guest working I can now
> reliably crash the hypervisor. No doubt this is a bug in my guest
> code, but I assume it shouldn't be possible for a buggy guest to take
> down Xen itself.
>
> Here's a simplified version of my code which shows the problem:
>
>    https://github.com/talex5/xen-paratest
>
> I'm building Xen from the stable-4.4 Git branch (03eb51340), compiled
> with debug on.
>
> The code is rather simple: it's just trying to initialise the data
> cache, as described in the "ARM Cortex-A Series Programmer’s Guide".
> I'm not actually sure whether this is necessary for a paravirtualised
> guest, but I was getting some odd problems which looked cache related,
> so I added this code in the hope of fixing that.

Does it crash if you remove your cache code?

>
> The cfg file is just:
>
> kernel = "/root/paratest.img"
> memory = 128
> name = "paratest"
> vcpus = 1
> serial="pty"
>
> When the guest is started, Xen always crashes. Sometimes silently, but
> usually writing a stack-trace to the console. I've included a
> selection of them in the commit messages, but a typical one looks like
> this:

hmmm, I've just tried your kernel on midway and Xen didn't crash.

Do you have more input? Number of physical CPUs used, state of the VCPU...?

>      (XEN) Assertion 'svc ==
> CSCHED_VCPU(curr_on_cpu(svc->vcpu->processor))' failed, line 859, file
> sche
>      (XEN) Xen BUG at sched_credit.c:859

I can't find any assert at this line. Did you modify Xen code?

>      (XEN) CPU1: Unexpected Trap: Undefined Instruction
>      (XEN) ----[ Xen-4.4.1-pre  arm32  debug=y  Not tainted ]----
>      (XEN) CPU:    1
>      (XEN) PC:     002417b4 __bug+0x28/0x44
>      (XEN) CPSR:   2000015a MODE:Hypervisor
>      (XEN)      R0: 002656dc R1: 00000000 R2: 3fd2bd80 R3: 2000015a
>      (XEN)      R4: 0000035b R5: 0025d9d0 R6: 40006230 R7: 47fe4be0
>      (XEN)      R8: 00265e00 R9: 002b1ff0 R10:002e4254 R11:47fd7e9c R12:00000001
>      (XEN) HYP: SP: 47fd7e94 LR: 002417b4
> [...]
>      (XEN) Xen call trace:
>      (XEN)    [<002417b4>] __bug+0x28/0x44 (PC)
>      (XEN)    [<002417b4>] __bug+0x28/0x44 (LR)
>      (XEN)    [<0021bac0>] csched_tick+0x1ac/0x4d4
>      (XEN)    [<0022d820>] execute_timer+0xcc/0xe0
>      (XEN)    [<0022d910>] timer_softirq_action+0xdc/0x230
>      (XEN)    [<00229b88>] __do_softirq+0xf4/0x100
>      (XEN)    [<00229c20>] do_softirq+0x14/0x18
>      (XEN)    [<0024f100>] leave_hypervisor_tail+0x50/0x6c
>      (XEN)    [<00251450>] return_to_guest+0xc/0xb8

Regards,


-- 
Julien Grall