Re: [Qemu-devel] [PATCH v4] migrate: Introduce a 'dc->vmsd' check to avoid segfault for --only-migratable

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Dr. David Alan Gilbert (dgilbert@redhat.com) wrote:
> * Ashijeet Acharya (ashijeetacharya@gmail.com) wrote:
> > Commit a3a3d8c7 introduced a segfault bug while checking for
> > 'dc->vmsd->unmigratable' which caused QEMU to crash when trying to add
> > devices which do no set their 'dc->vmsd' yet while initialization.
> > Place a 'dc->vmsd' check prior to it so that we do not segfault for
> > such devices.
> > 
> > NOTE: This doesn't compromise the functioning of --only-migratable
> > option as all the unmigratable devices do set their 'dc->vmsd'.
> > 
> > Introduce a new function check_migratable() and move the
> > only_migratable check inside it, also use stubs to avoid user-mode qemu
> > build failures.
> > 
> > Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
> 
> Yep, I think that should work.
> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Queued.

> 
> > ---
> > Changes in v4:
> > - introduce new check_migratable() function and use stubs
> > Changes is v3:
> > - move only_migratable check inside device_set_realized() to avoid code
> > - duplication
> > - I have dropped Juan's R-b tag for this one
> > Changes in v2:
> > - place dc->vmsd check in hw/usb/bus.c as well
> > ---
> >  hw/core/qdev.c                |  7 +++++++
> >  hw/usb/bus.c                  | 19 -------------------
> >  include/migration/migration.h |  3 +++
> >  migration/migration.c         | 15 +++++++++++++++
> >  qdev-monitor.c                |  9 ---------
> >  stubs/vmstate.c               |  6 ++++++
> >  6 files changed, 31 insertions(+), 28 deletions(-)
> > 
> > diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> > index 5783442..4f49cfe 100644
> > --- a/hw/core/qdev.c
> > +++ b/hw/core/qdev.c
> > @@ -37,6 +37,7 @@
> >  #include "hw/boards.h"
> >  #include "hw/sysbus.h"
> >  #include "qapi-event.h"
> > +#include "migration/migration.h"
> >  
> >  int qdev_hotplug = 0;
> >  static bool qdev_hot_added = false;
> > @@ -889,6 +890,7 @@ static void device_set_realized(Object *obj, bool value, Error **errp)
> >      Error *local_err = NULL;
> >      bool unattached_parent = false;
> >      static int unattached_count;
> > +    int ret;
> >  
> >      if (dev->hotplugged && !dc->hotpluggable) {
> >          error_setg(errp, QERR_DEVICE_NO_HOTPLUG, object_get_typename(obj));
> > @@ -896,6 +898,11 @@ static void device_set_realized(Object *obj, bool value, Error **errp)
> >      }
> >  
> >      if (value && !dev->realized) {
> > +        ret = check_migratable(obj, &local_err);
> > +        if (ret < 0) {
> > +            goto fail;
> > +        }
> > +
> >          if (!obj->parent) {
> >              gchar *name = g_strdup_printf("device[%d]", unattached_count++);
> >  
> > diff --git a/hw/usb/bus.c b/hw/usb/bus.c
> > index 1dcc35c..25913ad 100644
> > --- a/hw/usb/bus.c
> > +++ b/hw/usb/bus.c
> > @@ -8,7 +8,6 @@
> >  #include "monitor/monitor.h"
> >  #include "trace.h"
> >  #include "qemu/cutils.h"
> > -#include "migration/migration.h"
> >  
> >  static void usb_bus_dev_print(Monitor *mon, DeviceState *qdev, int indent);
> >  
> > @@ -687,8 +686,6 @@ USBDevice *usbdevice_create(const char *cmdline)
> >      const char *params;
> >      int len;
> >      USBDevice *dev;
> > -    ObjectClass *klass;
> > -    DeviceClass *dc;
> >  
> >      params = strchr(cmdline,':');
> >      if (params) {
> > @@ -723,22 +720,6 @@ USBDevice *usbdevice_create(const char *cmdline)
> >          return NULL;
> >      }
> >  
> > -    klass = object_class_by_name(f->name);
> > -    if (klass == NULL) {
> > -        error_report("Device '%s' not found", f->name);
> > -        return NULL;
> > -    }
> > -
> > -    dc = DEVICE_CLASS(klass);
> > -
> > -    if (only_migratable) {
> > -        if (dc->vmsd->unmigratable) {
> > -            error_report("Device %s is not migratable, but --only-migratable "
> > -                         "was specified", f->name);
> > -            return NULL;
> > -        }
> > -    }
> > -
> >      if (f->usbdevice_init) {
> >          dev = f->usbdevice_init(bus, params);
> >      } else {
> > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > index af9135f..a6868cd 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -22,6 +22,7 @@
> >  #include "qapi-types.h"
> >  #include "exec/cpu-common.h"
> >  #include "qemu/coroutine_int.h"
> > +#include "qom/object.h"
> >  
> >  #define QEMU_VM_FILE_MAGIC           0x5145564d
> >  #define QEMU_VM_FILE_VERSION_COMPAT  0x00000002
> > @@ -305,6 +306,8 @@ int migrate_add_blocker(Error *reason, Error **errp);
> >   */
> >  void migrate_del_blocker(Error *reason);
> >  
> > +int check_migratable(Object *obj, Error **err);
> > +
> >  bool migrate_postcopy_ram(void);
> >  bool migrate_zero_blocks(void);
> >  
> > diff --git a/migration/migration.c b/migration/migration.c
> > index 2766d2f..00b33f3 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -1146,6 +1146,21 @@ void migrate_del_blocker(Error *reason)
> >      migration_blockers = g_slist_remove(migration_blockers, reason);
> >  }
> >  
> > +int check_migratable(Object *obj, Error **err)
> > +{
> > +    DeviceClass *dc = DEVICE_GET_CLASS(obj);
> > +    if (only_migratable && dc->vmsd) {
> > +        if (dc->vmsd->unmigratable) {
> > +            error_setg(err, "Device %s is not migratable, but "
> > +                       "--only-migratable was specified",
> > +                       object_get_typename(obj));
> > +            return -1;
> > +        }
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> >  void qmp_migrate_incoming(const char *uri, Error **errp)
> >  {
> >      Error *local_err = NULL;
> > diff --git a/qdev-monitor.c b/qdev-monitor.c
> > index 549f45f..5f2fcdf 100644
> > --- a/qdev-monitor.c
> > +++ b/qdev-monitor.c
> > @@ -29,7 +29,6 @@
> >  #include "qemu/error-report.h"
> >  #include "qemu/help_option.h"
> >  #include "sysemu/block-backend.h"
> > -#include "migration/migration.h"
> >  
> >  /*
> >   * Aliases were a bad idea from the start.  Let's keep them
> > @@ -579,14 +578,6 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
> >          return NULL;
> >      }
> >  
> > -    if (only_migratable) {
> > -        if (dc->vmsd->unmigratable) {
> > -            error_setg(errp, "Device %s is not migratable, but "
> > -                       "--only-migratable was specified", driver);
> > -            return NULL;
> > -        }
> > -    }
> > -
> >      /* find bus */
> >      path = qemu_opt_get(opts, "bus");
> >      if (path != NULL) {
> > diff --git a/stubs/vmstate.c b/stubs/vmstate.c
> > index 6590627..5a71770 100644
> > --- a/stubs/vmstate.c
> > +++ b/stubs/vmstate.c
> > @@ -1,6 +1,7 @@
> >  #include "qemu/osdep.h"
> >  #include "qemu-common.h"
> >  #include "migration/vmstate.h"
> > +#include "migration/migration.h"
> >  
> >  const VMStateDescription vmstate_dummy = {};
> >  
> > @@ -18,3 +19,8 @@ void vmstate_unregister(DeviceState *dev,
> >                          void *opaque)
> >  {
> >  }
> > +
> > +int check_migratable(Object *obj, Error **err)
> > +{
> > +    return 0;
> > +}
> > -- 
> > 2.6.2
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK