Re: [PATCH v4 3/3] memory_hotplug.c: send DEVICE_UNPLUG_ERROR in acpi_memory_hotplug_write()

[Markus Armbruster]

Igor Mammedov <imammedo@redhat.com> writes:

> On Thu, 08 Jul 2021 15:08:57 +0200
> Markus Armbruster <armbru@redhat.com> wrote:
>
>> Daniel Henrique Barboza <danielhb413@gmail.com> writes:
>> 
>> > MEM_UNPLUG_ERROR is deprecated since the introduction of
>> > DEVICE_UNPLUG_ERROR. Keep emitting both while the deprecation of
>> > MEM_UNPLUG_ERROR is pending.
>> >
>> > CC: Michael S. Tsirkin <mst@redhat.com>
>> > CC: Igor Mammedov <imammedo@redhat.com>
>> > Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
>> > Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
>> > ---
>> >  hw/acpi/memory_hotplug.c | 13 +++++++++++--
>> >  1 file changed, 11 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/hw/acpi/memory_hotplug.c b/hw/acpi/memory_hotplug.c
>> > index af37889423..fb9f4d2de7 100644
>> > --- a/hw/acpi/memory_hotplug.c
>> > +++ b/hw/acpi/memory_hotplug.c
>> > @@ -8,6 +8,7 @@
>> >  #include "qapi/error.h"
>> >  #include "qapi/qapi-events-acpi.h"
>> >  #include "qapi/qapi-events-machine.h"
>> > +#include "qapi/qapi-events-qdev.h"
>> >  
>> >  #define MEMORY_SLOTS_NUMBER          "MDNR"
>> >  #define MEMORY_HOTPLUG_IO_REGION     "HPMR"
>> > @@ -177,9 +178,17 @@ static void acpi_memory_hotplug_write(void *opaque, 
>> > hwaddr addr, uint64_t data,
>> >              /* call pc-dimm unplug cb */
>> >              hotplug_handler_unplug(hotplug_ctrl, dev, &local_err);
>> >              if (local_err) {
>> > +                const char *error_pretty = error_get_pretty(local_err);
>> > +
>> >                  trace_mhp_acpi_pc_dimm_delete_failed(mem_st->selector);
>> > -                qapi_event_send_mem_unplug_error(dev->id,
>> > -                                                 
>> > error_get_pretty(local_err));
>> > +
>> > +                /*
>> > +                 * Send both MEM_UNPLUG_ERROR and DEVICE_UNPLUG_ERROR
>> > +                 * while the deprecation of MEM_UNPLUG_ERROR is
>> > +                 * pending.
>> > +                 */
>> > +                qapi_event_send_mem_unplug_error(dev->id, error_pretty);
>> > +                qapi_event_send_device_unplug_error(dev->id, 
>> > error_pretty);
>> >                  error_free(local_err);
>> >                  break;
>> >              }  
>> 
>> Same question as for PATCH 2: can dev->id be null?
> only theoretically (if memory device were created directly without
> using device_add), which as far as I know is not the case as all
> memory devices are created using -device/device_add so far.
>
> ( for device_add case see qdev_device_add->qdev_set_id where
>   'id' is set to user provided or to generated "device[%d]" value)

Something is set to a generated value, but it's not dev->id :)

    void qdev_set_id(DeviceState *dev, const char *id)

@id is the value of id=...  It may be null.

dev->id still is null here.

    {
        if (id) {
            dev->id = id;
        }

dev->id is now the value of id=...  It may be null.

        if (dev->id) {
            object_property_add_child(qdev_get_peripheral(), dev->id,
                                      OBJECT(dev));

If the user specified id=..., add @dev as child of /peripheral.  The
child's name is the (non-null) value of id=...

        } else {
            static int anon_count;
            gchar *name = g_strdup_printf("device[%d]", anon_count++);
            object_property_add_child(qdev_get_peripheral_anon(), name,
                                      OBJECT(dev));
            g_free(name);

Else, add @dev as child of /peripheral-anon.  The child's name is made
up.


        }
    }

dev->id is still the value of id=..., i.e. it may be null.

Sure dereferencing dev->id in acpi_memory_hotplug_write() is safe?