Re: [Qemu-devel] [PATCH] qom/cpu: Remove cpu->exit_request from reset state

[Andreas Färber]

Am 20.02.2014 16:58, schrieb Peter Maydell:
> On 16 February 2014 02:07, Edgar E. Iglesias <address@hidden> wrote:
>> On Sat, Feb 15, 2014 at 03:42:56PM +0000, Peter Maydell wrote:
>>> On 13 February 2014 05:07,  <address@hidden> wrote:
>>>> From: "Edgar E. Iglesias" <address@hidden>
>>>>
>>>> cpu->exit_request is part of the execution environment and should
>>>> not be cleared when a CPU resets.
>>>>
>>>> Otherwise, we might deadlock QEMU if a CPU resets while there is
>>>> I/O going on.
>>>>
>>>> Signed-off-by: Edgar E. Iglesias <address@hidden>
>>>> ---
>>>>  qom/cpu.c | 1 -
>>>>  1 file changed, 1 deletion(-)
>>>>
>>>> diff --git a/qom/cpu.c b/qom/cpu.c
>>>> index 9d62479..40d82dd 100644
>>>> --- a/qom/cpu.c
>>>> +++ b/qom/cpu.c
>>>> @@ -195,7 +195,6 @@ static void cpu_common_reset(CPUState *cpu)
>>>>          log_cpu_state(cpu, cc->reset_dump_flags);
>>>>      }
>>>>
>>>> -    cpu->exit_request = 0;
>>>>      cpu->interrupt_request = 0;
>>>>      cpu->current_tb = NULL;
>>>>      cpu->halted = 0;
>>>
>>> This looks kind of odd to me. What's the situation you see where
>>> this matters -- is the CPU resetting itself, or is some other device
>>> in another thread triggering the CPU reset? TCG or KVM?
>>
>> Seeing this in TCG. The CPU gets signaled by the IO thread while the
>> CPU is resetting itself. If the CPU looses the race, it clears its
>> exit_request leaving the IO thread waiting for the global lock
>> potentially forever.
>>
>> The CPU actually exits generated code but goes right back in because
>> there is no exit_request pending.
> 
> Yes, having looked at the code I agree with you, so:
> 
> Reviewed-by: Peter Maydell <address@hidden>

Thanks, applied to qom-cpu (with clarified commit message):
https://github.com/afaerber/qemu-cpu/commits/qom-cpu

Andreas

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