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

[Frederic Konrad]

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);
> > }