[Qemu-devel] Weird thing happen when the VM is stop! (0.12.3)

[Qemu-devel] Weird thing happen when the VM is stop! (0.12.3)

[Jun Koi]

Hi,

I found something very funny happening with 0.12.3: it seems the VM is
still running even I already stopped it.

Here is how I verified that: Boot any OS (I checked with Windows XP
and Ubuntu) with 0.12.3, and stop it any time after it booted up. Use
"stop" command on monitor interface.

Now the VM stops. Then in the same monitor interface, run "info
registers" again and again. You can see that the value of EIP and
EFLAGS still change once in a while. This should not happen, becaues
the VM already stopped.

I checked, and dont see this problem with 0.11.1. And this doesnt
happen with the latest code in the git tree, either.

Any idea on why this happens???

(My host is running Ubuntu 9.10, and I am using i386-softmmu/qemu to
run VM on this experiment)

Thanks,
Jun

Re: [Qemu-devel] Weird thing happen when the VM is stop! (0.12.3)

[Luiz Capitulino]

On Fri, 9 Apr 2010 18:32:21 +0900
Jun Koi <junkoi2004@gmail.com> wrote:

> Hi,
> 
> I found something very funny happening with 0.12.3: it seems the VM is
> still running even I already stopped it.
> 
> Here is how I verified that: Boot any OS (I checked with Windows XP
> and Ubuntu) with 0.12.3, and stop it any time after it booted up. Use
> "stop" command on monitor interface.
> 
> Now the VM stops. Then in the same monitor interface, run "info
> registers" again and again. You can see that the value of EIP and
> EFLAGS still change once in a while. This should not happen, becaues
> the VM already stopped.
> 
> I checked, and dont see this problem with 0.11.1. And this doesnt
> happen with the latest code in the git tree, either.
> 
> Any idea on why this happens???

 Can you try commit 55274a305 ? If it fixes the problem we need it
in stable, if it doesn't you can try to find the fix by using git bisect.

Re: [Qemu-devel] Weird thing happen when the VM is stop! (0.12.3)

[Jun Koi]

On Fri, Apr 9, 2010 at 10:20 PM, Luiz Capitulino <lcapitulino@redhat.com> wrote:
> On Fri, 9 Apr 2010 18:32:21 +0900
> Jun Koi <junkoi2004@gmail.com> wrote:
>
>> Hi,
>>
>> I found something very funny happening with 0.12.3: it seems the VM is
>> still running even I already stopped it.
>>
>> Here is how I verified that: Boot any OS (I checked with Windows XP
>> and Ubuntu) with 0.12.3, and stop it any time after it booted up. Use
>> "stop" command on monitor interface.
>>
>> Now the VM stops. Then in the same monitor interface, run "info
>> registers" again and again. You can see that the value of EIP and
>> EFLAGS still change once in a while. This should not happen, becaues
>> the VM already stopped.
>>
>> I checked, and dont see this problem with 0.11.1. And this doesnt
>> happen with the latest code in the git tree, either.
>>
>> Any idea on why this happens???
>
>  Can you try commit 55274a305 ? If it fixes the problem we need it
> in stable, if it doesn't you can try to find the fix by using git bisect.
>

This hint makes sense, but the point is that I tried with some commits
before that 55274a305, and didnt see the problem. Still I am not sure
the problem is already fixed before 55274a305, or I am just unlucky
enough not see the problem when testing.

After bisecting, I can say that the culprit is the below patch, from Marcelo.

Now I am wondering if the above commit 55274a305 of Paolo Bonzini
fixed the bug, or other commit before that?? We should find the
correct fix, and port it to 0.12.4.

Thanks,
J



commit 535d2eb34a0f1908dc694c51ce8d4ec6dccc7807
Author: Marcelo Tosatti <mtosatti@redhat.com>
Date:   Tue Feb 9 12:49:04 2010 -0200

    iothread: fix vcpu stop with smp tcg

    Round robin vcpus in tcg_cpu_next even if the vm stopped. This
    allows all cpus to enter stopped state.

    Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
    Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
    (cherry picked from commit c37cc7b072fa4ca8d8d21ac31d26baff5f47f9f9)

diff --git a/vl.c b/vl.c
index 007709a..3b5a8e0 100644
--- a/vl.c
+++ b/vl.c
@@ -4042,14 +4042,15 @@ static void tcg_cpu_exec(void)
     for (; next_cpu != NULL; next_cpu = next_cpu->next_cpu) {
         CPUState *env = cur_cpu = next_cpu;

-        if (!vm_running)
-            break;
         if (timer_alarm_pending) {
             timer_alarm_pending = 0;
             break;
         }
         if (cpu_can_run(env))
             ret = qemu_cpu_exec(env);
+        else if (env->stop)
+            break;
+
         if (ret == EXCP_DEBUG) {
             gdb_set_stop_cpu(env);
             debug_requested = 1;

Re: [Qemu-devel] Weird thing happen when the VM is stop! (0.12.3)

[Marcelo Tosatti]

On Sat, Apr 10, 2010 at 01:12:27AM +0900, Jun Koi wrote:
> On Fri, Apr 9, 2010 at 10:20 PM, Luiz Capitulino <lcapitulino@redhat.com> wrote:
> > On Fri, 9 Apr 2010 18:32:21 +0900
> > Jun Koi <junkoi2004@gmail.com> wrote:
> >
> >> Hi,
> >>
> >> I found something very funny happening with 0.12.3: it seems the VM is
> >> still running even I already stopped it.
> >>
> >> Here is how I verified that: Boot any OS (I checked with Windows XP
> >> and Ubuntu) with 0.12.3, and stop it any time after it booted up. Use
> >> "stop" command on monitor interface.
> >>
> >> Now the VM stops. Then in the same monitor interface, run "info
> >> registers" again and again. You can see that the value of EIP and
> >> EFLAGS still change once in a while. This should not happen, becaues
> >> the VM already stopped.
> >>
> >> I checked, and dont see this problem with 0.11.1. And this doesnt
> >> happen with the latest code in the git tree, either.
> >>
> >> Any idea on why this happens???
> >
> >  Can you try commit 55274a305 ? If it fixes the problem we need it
> > in stable, if it doesn't you can try to find the fix by using git bisect.
> >
> 
> This hint makes sense, but the point is that I tried with some commits
> before that 55274a305, and didnt see the problem. Still I am not sure
> the problem is already fixed before 55274a305, or I am just unlucky
> enough not see the problem when testing.
> 
> After bisecting, I can say that the culprit is the below patch, from Marcelo.
> 
> Now I am wondering if the above commit 55274a305 of Paolo Bonzini
> fixed the bug, or other commit before that?? We should find the
> correct fix, and port it to 0.12.4.

Guess its c5f32c99. Can you confirm please?

Re: [Qemu-devel] Weird thing happen when the VM is stop! (0.12.3)

[Jun Koi]

On Sat, Apr 10, 2010 at 3:09 AM, Marcelo Tosatti <mtosatti@redhat.com> wrote:
> On Sat, Apr 10, 2010 at 01:12:27AM +0900, Jun Koi wrote:
>> On Fri, Apr 9, 2010 at 10:20 PM, Luiz Capitulino <lcapitulino@redhat.com> wrote:
>> > On Fri, 9 Apr 2010 18:32:21 +0900
>> > Jun Koi <junkoi2004@gmail.com> wrote:
>> >
>> >> Hi,
>> >>
>> >> I found something very funny happening with 0.12.3: it seems the VM is
>> >> still running even I already stopped it.
>> >>
>> >> Here is how I verified that: Boot any OS (I checked with Windows XP
>> >> and Ubuntu) with 0.12.3, and stop it any time after it booted up. Use
>> >> "stop" command on monitor interface.
>> >>
>> >> Now the VM stops. Then in the same monitor interface, run "info
>> >> registers" again and again. You can see that the value of EIP and
>> >> EFLAGS still change once in a while. This should not happen, becaues
>> >> the VM already stopped.
>> >>
>> >> I checked, and dont see this problem with 0.11.1. And this doesnt
>> >> happen with the latest code in the git tree, either.
>> >>
>> >> Any idea on why this happens???
>> >
>> >  Can you try commit 55274a305 ? If it fixes the problem we need it
>> > in stable, if it doesn't you can try to find the fix by using git bisect.
>> >
>>
>> This hint makes sense, but the point is that I tried with some commits
>> before that 55274a305, and didnt see the problem. Still I am not sure
>> the problem is already fixed before 55274a305, or I am just unlucky
>> enough not see the problem when testing.
>>
>> After bisecting, I can say that the culprit is the below patch, from Marcelo.
>>
>> Now I am wondering if the above commit 55274a305 of Paolo Bonzini
>> fixed the bug, or other commit before that?? We should find the
>> correct fix, and port it to 0.12.4.
>
> Guess its c5f32c99. Can you confirm please?

I back-ported this patch to 0.12.3, and it seems the problem is gone.

Thanks,
J