Re: [Qemu-devel] [RFC PATCH 1/3] cpus: protect queued_work_* with work_mutex.

[Frederic Konrad <fred.konrad@greensocs.com>]

On 10/07/2015 17:34, Paolo Bonzini wrote:
>
> On 10/07/2015 17:32, Frederic Konrad wrote:
>> I think something like that can work because we don't have two
>> flush_queued_work at the same time on the same CPU?
> Yes, this works; there is only one consumer.
>
> Holding locks within a callback can be very painful, especially if there
> is a chance that the callback will take a very coarse lock such as big
> QEMU lock.  It can cause AB-BA deadlocks.
>
> Paolo

Ok fine I'll change that.

Fred
>
>> static void flush_queued_work(CPUState *cpu)
>> {
>>      struct qemu_work_item *wi;
>>
>>      if (cpu->queued_work_first == NULL) {
>>          return;
>>      }
>>
>>      qemu_mutex_lock(&cpu->work_mutex);
>>      while ((wi = cpu->queued_work_first)) {
>>          cpu->queued_work_first = wi->next;
>>          qemu_mutex_unlock(&cpu->work_mutex);
>>          wi->func(wi->data);
>>          qemu_mutex_lock(&cpu->work_mutex);
>>          wi->done = true;
>>          if (wi->free) {
>>              g_free(wi);
>>          }
>>      }
>>      cpu->queued_work_last = NULL;
>>      qemu_mutex_unlock(&cpu->work_mutex);
>>
>>      qemu_cond_broadcast(&qemu_work_cond);
>> }