Re: Crashes with qemu-system-ppc64

[Philippe Mathieu-Daudé]

On 3/24/21 12:00 AM, Greg Kurz wrote:
> Cc'ing David
> 
> On Tue, 23 Mar 2021 17:48:36 +0100
> Thomas Huth <thuth@redhat.com> wrote:
> 
>>
>> In case anyone is interested in fixing those, there are two regressions with 
>> qemu-system-ppc64 in the current master branch:
>>
>> $ ./qemu-system-ppc64 -M ppce500 -device macio-oldworld
>> qemu-system-ppc64: ../../devel/qemu/softmmu/memory.c:2443: 
>> memory_region_add_subregion_common: Assertion `!subregion->container' failed.
>>
>> $ ./qemu-system-ppc64 -device power8_v2.0-spapr-cpu-core,help
>> /home/thuth/devel/qemu/include/hw/boards.h:24:MACHINE: Object 0x5635bd53af10 
>> is not an instance of type machine
>> Aborted (core dumped)
>>
> 
> I've bisected this one to:
> 
> 3df261b6676b5850e93d6fab3f7a98f8ee8f19c5 is the first bad commit
> commit 3df261b6676b5850e93d6fab3f7a98f8ee8f19c5
> Author: Peter Maydell <peter.maydell@linaro.org>
> Date:   Fri Mar 13 17:24:47 2020 +0000
> 
>     softmmu/vl.c: Handle '-cpu help' and '-device help' before 'no default 
> machine'
>     
>     Currently if you try to ask for the list of CPUs for a target
>     architecture which does not specify a default machine type
>     you just get an error:
>     
>       $ qemu-system-arm -cpu help
>       qemu-system-arm: No machine specified, and there is no default
>       Use -machine help to list supported machines
>     
>     Since the list of CPUs doesn't depend on the machine, this is
>     unnecessarily unhelpful. "-device help" has a similar problem.
>     
>     Move the checks for "did the user ask for -cpu help or -device help"
>     up so they precede the select_machine() call which checks that the
>     user specified a valid machine type.
>     
>     Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> 
>  softmmu/vl.c | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)
> bisect run success
> 
> This change is fine but it unveils a bad assumption.
> 
> 0  0x00007ffff64a3708 in raise () at /lib64/power9/libc.so.6
> #1  0x00007ffff6483bcc in abort () at /lib64/power9/libc.so.6
> #2  0x00000001008db940 in object_dynamic_cast_assert
>     (obj=0x10126f670, typename=0x100c20380 "machine", file=0x100b34878 
> "/home/greg/Work/qemu/qemu-ppc/include/hw/boards.h", line=<optimized out>, 
> func=0x100bcd320 <__func__.30338> "MACHINE") at ../../qom/object.c:883
> #3  0x0000000100456e00 in MACHINE (obj=<optimized out>) at 
> /home/greg/Work/qemu/qemu-ppc/include/hw/boards.h:24
> #4  0x0000000100456e00 in cpu_core_instance_init (obj=0x10118e2c0) at 
> ../../hw/cpu/core.c:69
> #5  0x00000001008d9f44 in object_init_with_type (obj=obj@entry=0x10118e2c0, 
> ti=0x1011fd470) at ../../qom/object.c:375
> #6  0x00000001008d9f24 in object_init_with_type (obj=obj@entry=0x10118e2c0, 
> ti=0x101211ad0) at ../../qom/object.c:371
> #7  0x00000001008d9f24 in object_init_with_type (obj=obj@entry=0x10118e2c0, 
> ti=ti@entry=0x101212760) at ../../qom/object.c:371
> #8  0x00000001008dc474 in object_initialize_with_type 
> (obj=obj@entry=0x10118e2c0, size=size@entry=160, type=type@entry=0x101212760) 
> at ../../qom/object.c:517
> #9  0x00000001008dc678 in object_new_with_type (type=0x101212760) at 
> ../../qom/object.c:732
> #10 0x00000001009fbad8 in qmp_device_list_properties (typename=<optimized 
> out>, errp=<optimized out>) at ../../qom/qom-qmp-cmds.c:146
> #11 0x00000001005a4bf0 in qdev_device_help (opts=0x10126c200) at 
> ../../softmmu/qdev-monitor.c:285
> #12 0x0000000100760afc in device_help_func (opaque=<optimized out>, 
> opts=<optimized out>, errp=<optimized out>) at ../../softmmu/vl.c:1204
> #13 0x0000000100ad1050 in qemu_opts_foreach (list=<optimized out>, 
> func=0x100760ae0 <device_help_func>, opaque=0x0, errp=0x0) at 
> ../../util/qemu-option.c:1167
> #14 0x00000001007653cc in qemu_process_help_options () at 
> ../../softmmu/vl.c:2451
> #15 0x00000001007653cc in qemu_init (argc=<optimized out>, argv=<optimized 
> out>, envp=<optimized out>) at ../../softmmu/vl.c:3521
> #16 0x00000001002f4f88 in main (argc=<optimized out>, argv=<optimized out>, 
> envp=<optimized out>) at ../../softmmu/main.c:49
> 
> Basically, "-device power8_v2.0-spapr-cpu-core,help" ends up
> instantiating an object of the "power8_v2.0-spapr-cpu-core" type,
> which derives from "cpu-core". The "cpu-core" type has an instance
> init function that assumes that qdev_get_machine() returns an object
> of type "machine"...
> 
> static void cpu_core_instance_init(Object *obj)
> {
>     MachineState *ms = MACHINE(qdev_get_machine());
>                          ^^
>                      ...here.
> 
> qdev_get_machine() cannot return a valid machine type since
> select_machine() hasn't been called yet... an instance init
> function is probably not the best place to use qdev_get_machine()
> if any.

Hmmm does this assert() matches your comment?

-- >8 --
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index cefc5eaa0a9..41cbee77d14 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -1130,6 +1130,8 @@ Object *qdev_get_machine(void)
 {
     static Object *dev;

+    assert(phase_check(PHASE_MACHINE_CREATED));
+
     if (dev == NULL) {
         dev = container_get(object_get_root(), "/machine");
     }
---

> 
>     CPUCore *core = CPU_CORE(obj);
> 
>     core->nr_threads = ms->smp.threads;
> }
> 
> It seems that this should rather sit in a device realize function,
> when the machine type is known.
> 
>>   Thomas
>>
>>
> 
>