Re: [Qemu-devel] [PATCH 1/2] spapr_cpu_core: instantiate CPUs separately

[Greg Kurz <groug@kaod.org>]

On Fri, 13 Oct 2017 11:21:20 +0200
Igor Mammedov <imammedo@redhat.com> wrote:

> On Fri, 13 Oct 2017 10:35:19 +0200
> Greg Kurz <groug@kaod.org> wrote:
> 
> > The current code assumes that only the CPU core object holds a
> > reference on each individual CPU object, and happily frees their
> > allocated memory when the core is unrealized. This is dangerous
> > as some other code can legitimely keep a pointer to a CPU if it
> > calls object_ref(), but it would end up with a dangling pointer.
> > 
> > Let's allocate all CPUs with object_new() and let QOM frees them
> > when their reference count reaches zero.  
> I agree with patch as it simplifies code and one doesn't have to
> fiddle wit size anymore.

Yes, I'll mention that in the changelog as well.

> See some comments below.
> 
> > 
> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> >  hw/ppc/spapr.c                  |   10 +++-------
> >  hw/ppc/spapr_cpu_core.c         |   29 +++++++++--------------------
> >  include/hw/ppc/spapr_cpu_core.h |    2 +-
> >  3 files changed, 13 insertions(+), 28 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index fd9813bde82f..ba391c6ed5de 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -3153,12 +3153,10 @@ void spapr_core_release(DeviceState *dev)
> >  
> >      if (smc->pre_2_10_has_unused_icps) {
> >          sPAPRCPUCore *sc = SPAPR_CPU_CORE(OBJECT(dev));
> > -        sPAPRCPUCoreClass *scc = SPAPR_CPU_CORE_GET_CLASS(OBJECT(cc));
> > -        size_t size = object_type_get_instance_size(scc->cpu_type);
> >          int i;
> >  
> >          for (i = 0; i < cc->nr_threads; i++) {
> > -            CPUState *cs = CPU(sc->threads + i * size);
> > +            CPUState *cs = CPU(sc->threads[i]);
> >  
> >              pre_2_10_vmstate_register_dummy_icp(cs->cpu_index);
> >          }
> > @@ -3204,7 +3202,7 @@ static void spapr_core_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
> >      sPAPRMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
> >      sPAPRCPUCore *core = SPAPR_CPU_CORE(OBJECT(dev));
> >      CPUCore *cc = CPU_CORE(dev);
> > -    CPUState *cs = CPU(core->threads);
> > +    CPUState *cs = CPU(core->threads[0]);
> >      sPAPRDRConnector *drc;
> >      Error *local_err = NULL;
> >      int smt = kvmppc_smt_threads();
> > @@ -3249,13 +3247,11 @@ static void spapr_core_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
> >      core_slot->cpu = OBJECT(dev);
> >  
> >      if (smc->pre_2_10_has_unused_icps) {
> > -        sPAPRCPUCoreClass *scc = SPAPR_CPU_CORE_GET_CLASS(OBJECT(cc));
> > -        size_t size = object_type_get_instance_size(scc->cpu_type);
> >          int i;
> >  
> >          for (i = 0; i < cc->nr_threads; i++) {
> >              sPAPRCPUCore *sc = SPAPR_CPU_CORE(dev);
> > -            void *obj = sc->threads + i * size;
> > +            void *obj = sc->threads[i];
> >  
> >              cs = CPU(obj);
> >              pre_2_10_vmstate_unregister_dummy_icp(cs->cpu_index);
> > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > index 3a4c17401226..47c408b52ca1 100644
> > --- a/hw/ppc/spapr_cpu_core.c
> > +++ b/hw/ppc/spapr_cpu_core.c
> > @@ -79,21 +79,18 @@ const char *spapr_get_cpu_core_type(const char *cpu_type)
> >  static void spapr_cpu_core_unrealizefn(DeviceState *dev, Error **errp)
> >  {
> >      sPAPRCPUCore *sc = SPAPR_CPU_CORE(OBJECT(dev));
> > -    sPAPRCPUCoreClass *scc = SPAPR_CPU_CORE_GET_CLASS(OBJECT(dev));
> > -    size_t size = object_type_get_instance_size(scc->cpu_type);
> >      CPUCore *cc = CPU_CORE(dev);
> >      int i;
> >  
> >      for (i = 0; i < cc->nr_threads; i++) {
> > -        void *obj = sc->threads + i * size;
> > -        DeviceState *dev = DEVICE(obj);
> > +        DeviceState *dev = DEVICE(sc->threads[i]);
> >          CPUState *cs = CPU(dev);
> >          PowerPCCPU *cpu = POWERPC_CPU(cs);
> >  
> >          spapr_cpu_destroy(cpu);
> >          object_unparent(cpu->intc);
> >          cpu_remove_sync(cs);
> > -        object_unparent(obj);
> > +        object_unparent(sc->threads[i]);
> >      }
> >      g_free(sc->threads);
> >  }
> > @@ -146,9 +143,7 @@ static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
> >      sPAPRCPUCore *sc = SPAPR_CPU_CORE(OBJECT(dev));
> >      sPAPRCPUCoreClass *scc = SPAPR_CPU_CORE_GET_CLASS(OBJECT(dev));
> >      CPUCore *cc = CPU_CORE(OBJECT(dev));
> > -    size_t size;
> >      Error *local_err = NULL;
> > -    void *obj;
> >      int i, j;
> >  
> >      if (!spapr) {
> > @@ -156,17 +151,14 @@ static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
> >          return;
> >      }
> >  
> > -    size = object_type_get_instance_size(scc->cpu_type);
> > -    sc->threads = g_malloc0(size * cc->nr_threads);
> > +    sc->threads = g_new(void *, cc->nr_threads);  
> 
>                            ^^^ PowerPCCPU*
> 

Right, I guess void * was appropriate to do the pointer arithmetics but we don't
need that anymore.

> and maybe g_new0() if incomplete cores are possible.
> 

Yes, older machine types (ie, that don't support CPU hotplug) can have
incomplete cores, but cc->nr_threads is set to the actual number of
threads in this case. See spapr_init_cpus() in hw/ppc/spapr.c.

> >      for (i = 0; i < cc->nr_threads; i++) {
> >          char id[32];
> >          CPUState *cs;
> >          PowerPCCPU *cpu;
> >  
> > -        obj = sc->threads + i * size;
> > -
> > -        object_initialize(obj, size, scc->cpu_type);
> > -        cs = CPU(obj);
> > +        sc->threads[i] = object_new(scc->cpu_type);
> > +        cs = CPU(sc->threads[i]);
> >          cpu = POWERPC_CPU(cs);
> >          cs->cpu_index = cc->core_id + i;
> >          cpu->vcpu_id = (cc->core_id * spapr->vsmt / smp_threads) + i;
> > @@ -184,17 +176,15 @@ static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
> >          cpu->node_id = sc->node_id;
> >  
> >          snprintf(id, sizeof(id), "thread[%d]", i);
> > -        object_property_add_child(OBJECT(sc), id, obj, &local_err);
> > +        object_property_add_child(OBJECT(sc), id, sc->threads[i], &local_err);
> >          if (local_err) {
> >              goto err;
> >          }
> > -        object_unref(obj);
> > +        object_unref(sc->threads[i]);
> >      }
> >  
> >      for (j = 0; j < cc->nr_threads; j++) {
> > -        obj = sc->threads + j * size;
> > -
> > -        spapr_cpu_core_realize_child(obj, spapr, &local_err);
> > +        spapr_cpu_core_realize_child(sc->threads[j], spapr, &local_err);
> >          if (local_err) {
> >              goto err;
> >          }
> > @@ -203,8 +193,7 @@ static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
> >  
> >  err:
> >      while (--i >= 0) {
> > -        obj = sc->threads + i * size;
> > -        object_unparent(obj);
> > +        object_unparent(sc->threads[i]);
> >      }
> >      g_free(sc->threads);
> >      error_propagate(errp, local_err);
> > diff --git a/include/hw/ppc/spapr_cpu_core.h b/include/hw/ppc/spapr_cpu_core.h
> > index f2d48d6a6786..f5b943a6682c 100644
> > --- a/include/hw/ppc/spapr_cpu_core.h
> > +++ b/include/hw/ppc/spapr_cpu_core.h
> > @@ -28,7 +28,7 @@ typedef struct sPAPRCPUCore {
> >      CPUCore parent_obj;
> >  
> >      /*< public >*/
> > -    void *threads;
> > +    void **threads;  
> ditto, should be PowerPCCPU
> 

Ok.

Thanks for the feedback!

> >      int node_id;
> >  } sPAPRCPUCore;
> >  
> > 
> >   
>